Eye Colors



Bring pigeons eyes up as a topic for discussion between a group of pigeon fanciers and you'll be amazed at the different responses you get.   Some will jump right into the pros and cons of the various "Eye Sign" theories as a performance indicator while others will point to the genetically different eye colors and how to breed for color to achieve the show standards required for the many different breed types.    Both of these topics are highly debated and for some reason very few will agree on either subject.   Why is there such disagreement?   To me the answer is simple.   There isn't enough scientific research conducted on "Eye Sign" to come to their final conclusions nor is there enough factual information published on "Genetics" to explain eye colors.     The eye sign enthusiasts have done an excellent job publishing books, pamphlets and videos to get the word out but they don't always agree with each others findings.  They all admit to there being exceptions to every rule but that's not how science works.   In true science there are no exceptions to any rule without clear understandable causes and those causes should be both explainable and demonstrable.    

Back somewhere around 1947, when I was only six years old, pigeon men here in the U.S. began hearing and reading about the secrets of eye sign.   This is not to say that the subject isn't much older because it may very well be.  However, it wasn't until after World War II that eye sign took this country’s pigeon enthusiasts by storm.  A few self proclaimed experts began publishing their books and gave their demonstrations and presto, the quest for the secrets contained in the eye was on. 

Naturally flyers of that day, like my Grandfather, began looking into the eyes of their pigeons to discover their bird’s potential as both racers and or breeders.  I'm sure, for them, it was a fascinating subject just as it is today.

Theories were put forward and terms like the circle of adaptation, circle of correlation, speed lines, distance lines, breeding grooves etc. just to name a few became the topic of discussion at the local gathering places.

These theories were not limited to pigeon racers only, as other performing breeds such as rollers and highflyers were soon to follow in that same pursuit.

Today there are many books and videos to explain the various eye sign theories but until they are scientifically proven or disproved, these theories remain theories.   They still require the correct type of research under controlled conditions to be conducted.   When that happens the findings that support their claims can be made as proven facts.    Until then, Eye Sign will remain today what it has been for years and that is simply personal opinions and or theories.  

Of the two subjects, "Eye Sign" and "Eye Color Genetics"  the genetic side has the only proof of controlled scientific research to back their findings.   Now having said all that, let me also make this point very clear.  These two subjects are not in competition.  They address entirely different issues; however, genetic findings that are accepted as proven facts should play a roll in the eye sign advice given for breeding eye colors.  Unfortunately they don't and I'll address that more as we get into it.

True there are still unanswered questions in genetics that relate to the more uncommon eye colors but by in large most of the mystery of eye color genetics has been solved and it was solved many years ago.  What's needed now, is to get the word out to the everyday fanciers and I am trying to accomplish some of that here.

In other words, our subject is going to be based on the " Genetics of eye colors ".   I'll leave the topic of "Eye Sign" as a performance indicator for others like my good friend Nigel Cowood.   In the sport of racing pigeons, it seems to work very well for him and his video does show what to look for in detail.   Therefore, I'll leave it to other enthusiasts like Nigel to ring that bell.

A discussion of pigeon eye color genetics

A discussion of pigeon color genetics, be it for feather color or eye color, simply wouldn't be complete without first recognizing the work of Dr. W.F. Hollander.    Dr. Hollander may not have been the first to study these things but he is without doubt the foremost leading expert to have done so.  He specialized in poultry, mice and fruit flies but his personal love was pigeons.   He was without doubt the world's most knowledgeable person to ever study pigeons and study them he did with a passion.

In his book "Origins and Excursions in Pigeon Genetics," Dr. Hollander points out that the most significant genetic differences of eye colors are orange, pearl, and bull.  The first two, orange and pearl (sometimes referred to as yellow and white) deal with pigment found in the outer side of the iris, while the third; bull, deals with the pigment found on the iris's inner side.  Pigment found on the inner side of the iris is only visible when the outer pigment is missing.   So as far as the pigeon's eyes are concerned, only two known pigment types (orange and pearl) are possible on the outer iris  and only one pigment type is possible on the inner surface.  This inner surface when visible has a dark almost black look similar to the effect seen on cattle thus the name bull eye.  

Hollander was not the first to study these colors.    A number of European students prior to 1930 had already done so.  Of these, the most pertinent was a S. J. Bessmertnaja who in Russian demonstrated that when you cross birds that were known to be pure for orange eyed with birds pure for pearl, only  orange eyed F1 youngsters were produced.   He went on to demonstrate that when you crossed one of the orange eyed F1's back to a pearl that both colors, orange or pearl  could result.   He did this using only ten such crosses.  He concluded from his work that pearl was a simple recessive gene and symbolized it tr. 

If you're a student of genetics, you will soon learn that when two genetic factors are alleles (separate possibilities), like orange eye and pearl eye,  then one is going to be recessive to the other.  In such case, the recessive one will only display when homozygous or pure while the dominant of the two will display in either condition be it heterozygous split for both or homozygous pure for both.   Bessmertnaja's crosses did indicate this but the relatively small number of test crosses (10) were not sufficient to rule out other possibilities.   So Dr. Hollander along with an associate R. D. Owen conducted more crosses using far more conclusive numbers.  From this far greater study with more extensive data, they were able to confirm Bessmertnaja work.  In addition, they also discovered that a sort of imitation pearl effect was produced by the sex-linked brown feather color gene on genetically orange eyed birds.  In other words, the gene that produces the brown plumage would also produce a pearl iris color that is an intrinsic effect, one not involving the pearl or tr gene.   Several years later, Dr. Hollander went on to discover that another imitation pearl effect was also produced by the rare albino and pink-eyed-dilute genes.

Lets pause for a moment and review how these two gene alleles are reproduced in a selective breeding program.  If you're not up on the fundamentals of reproduction please go back and review the two chapters

 Sex, Chromosomes and Genes and  Cell Reproduction, Mitosis, Meiosis and Crossovers

Ok you read it, now lets put it to the test .  Get four white buttons and four orange buttons.  These will be our stock pile of gene possibilities for eye colors between two breeding adults. In the test we will only need a total of two each per breeder or a total of four for the pair.  put two buttons in one hand and two in the other. Let the buttons in one hand represent one bird and the other hand the other bird.  Now slightly open each hand and let only one button form each hand fall to the ground. The combination of the two buttons on the floor represent the youngster's genes for eye color. No matter how many times you run the test, the outcome for these different genetic possibilities will be the same as those shown here to the right.  Its just a simple matter of probabilities.

Using four orange buttons lets begin by pairing together two orange eyed birds.

Homozygous orange x homozygous orange = 100% pure homozygous orange.   The end result is orange eyes.

Then pair an orange eyed pigeon that is heterozygous for both eye colors with a pure pearl eyed pigeon.   Note that there are two possibilities for this type of cross.


Heterozygous orange x homozygous pearl = 50% for both orange and pearl (resulting in orange eyes) and 50% pure homozygous pearl (resulting in pearl eyes).

Next pair two orange eyed pigeons where they are both heterozygous for both orange and pearl.  There are four possibilities here and all but one are in the orange eye color.

Heterozygous orange x heterozygous pearl = 25% pure homozygous orange (resulting in orange eyes)
50% heterozygous for both orange and pearl (resulting in orange eyes)
25% pure homozygous pearl (resulting in pearl eyes).

Now lets pair a pure orange with a pure pearl.

Homozygous orange x homozygous pearl =
100% for both orange and pearl (resulting in orange eyes)

And lastly lets pair two pure or homozygous pearl birds together.

Homozygous pearl x homozygous pearl =
100% homozygous pearl (resulting in pearl eyes).

Did you notice the possibility for orange eye is greater than the possibility for pearl; or that all pearl eyed pigeons are pure for their pearl eyed gene, regardless of what color their parents eyes were?

I want you to remember this and remember it well.  When you read eye sign experts who write "yellow x pearl gives you a superior pearl eye, while pearl x pearl is a weaker eye" such advice is pure baloney!!!  

These kinds of old wives tail should alert you to the writer's ignorance on genetic matters.   There are no genetic differences between pearl eyes based solely upon how they were produced.    A pearl eyed pigeon is pearl eyed whenever a single gene factor for pearl is transmitted from both parents to their offspring.    It is simply immaterial  what other genetic possibilities being carried by either parent might have been, as that material was not what was passed along to the youngster.  

The existence or presence of something not transmitted; nor the absence of something not received is of no consequence.   It is only that genetic material, which was transmitted that is of any consequence.    All pigeons with pearl eyes are pure for the pearl eye trait regardless of what their parents eye color was. For any pigeon to be a pearl eyed bird it had to receive one pearl gene from each parent regardless if those parents were both yellow eyed carrying pearl; or if one was yellow carrying pearl and the other pure for pearl; or even if both were pure pearl eyed pigeons themselves.  Pure is pure 100% of the time.  


Orange and Pearl eyes


Orange (yellow)eye                   Pearl (white) eye

Some eyes are much lighter and brighter than others and some have far grater amounts of red color in the iris.  Sometime this red is so grate that the orange or pearl can barely be seen.   Sometimes orange is referred to as a yellow eye, while pearl is referred to as white or even fish eyed.   Why is this?   The answer lies in the amount of blood found in the different variations of these two eye colors.


False pearl of brown                       Yellow eye

Dr. Hollander in his book Origins and Excursions in Pigeon Genetics, put it this way.

"Orange is the wild-type iris color of Columba livia, and most feral street pigeons and those in farm flocks have this color. Pearl is strictly a domestic type, some breeds such as Tumblers and Barbs never having orange eyes.   Microscopic study has shown that the only difference is in the fine pigment granules on the outer surface of the iris: they are yellow in the wild type, and white in the pearl eye.


In addition to the granular pigment, the iris is covered in varying degree with a spaghetti-like mass of tiny blood vessels.    These give the iris a reddening effect. Anemia will cause paleness.  And some breeds have been selected for minimal blood vessel coverage.    For example, the American Domestic Flight has a staring white "fish" eye, but basically it is pearl type.

So from these two basic pigment colors we can produce eyes that are yellow, orange, fiery red orange, white or fish eyed, pearl and fiery red pearl or any of the many variations in-between.    Their differences all being the result of two pigment colors yellow and white (orange and pearl) and the varying amounts of blood present on the surface of the iris.

However, today we do find birds with other eye colors such as green violet and even dark brown but proof that these are the result of additional iris pigments has not been demonstrated.  They may be new alleles to yellow and pearl or they may simply be modifiers to them.  We need more data to learn the answers.

One could safely say that any of the flying breeds which require long grueling endurance would be those of greater blood circulation. Increased vascular capability or decreased anemia are signs of endurance potential but are they only limited to the eye?  If they extend to the body as a whole then yes the eye could be a good indicator of grueling performance like racing. In other words the redder the eyes the greater the potential is for eye sign features like circle of adaptation, circle of correlation, speed lines, distance lines and breeding grooves in addition to the increase in endurance potential due to improved vascular blood flow.   The question remains, does this increase or lack thereof extend to the body as a whole and how does it relate to homing navigation, rolling, speed in flight and breeding skills?    I do not have those answers.

Before we leave the subject of pearl eyes; I would like to also point out that Dr.Hollander was of the opinion that the pearl eye color is a very ancient mutation.  He believed it was originally found only in cretin breeds from Persia. Granted modern day cross breeding has  changed some of these breeds eye colors that he has  listed as being found only in pearl.  Here is how he defined its origins.

"The origin of pearl probably was very ancient.  My guess is that it was picked up by fanciers before the tumbling trait, since all Tumblers, Rollers, and Highfliers so far as I know are homozygous for tr-(Some exceptions are known in can readily be explain¬ed by crossing.)   Related breeds having only pearl eye are the Nun, Helmet, Jacobin, and Magpie.   The Barb possibly had Tumbler far back in its ancestry."

"Pearl is also common in breeds not closely related to Tumblers.   Show Homers and Exhibition Homers are all pearl-eyed; other Homers often have pearl, but Carriers and Dragoons do not.   Runts, Fantails, and some Continental varieties of Pouters, Trumpeters, and Archangels often have pearl iris. "

Breeds never showing pearl, so far as I know, are English Carriers, Dragoons, English Pouters, Modenas, Maltese, Florentines, Hungarians, Strassers, Carneaux (except some Whites), Dewlaps, Damascenes, Swifts, Owls, Blondinettes, Frillbacks, German Toys, Lynx, and the Kings.   I know little of the eye color of Chinese breeds."

"From this breed distribution it seems unlikely that pearl originated in Europe, or even in the Mediterranean region.  Persia seems a good bet -- the place we seem to trace many things back to.   Back in those ancient times fanciers must have been peering into the mysteries of the eye too, without benefit of magnifying glasses, but they found a pearl."

Origins and excursions in pigeon genetics page 78, Xlll. PEARL EYE (also -- NPA News, March 1964, page 7)
by W.F. Hollander

 Bull eyes


Bull eye is similar in appearance to the dark eyes of most cattle; that's where this bull eye color gets its name. Bull eyes are not a substitute for either orange or pearl but rather only results when the orange or pearl pigment has been turned off; thus allowing light to pass thru the outer iris pigment, deeper into the eye and reflect the darker pigment of the inner surface's of the eye. Genetically, a bull eyed pigeon is still an orange or pearl eyed bird, however; the pigment production (orange or pearl) on the outer surface of the iris has simply been switched off by the pied white gene.  

OK; fine, but which genes can switch off the iris outer surface pigment production to display a bull eye?   Good question and the answer is genes that produce Recessive White and Pied Bald White are the most common causes of no pigment on the skin, beak, toe nails and outer surfaces of the eye. These genes turn off the production of pigment at the body surface level and this in turn prevent both feathers from producing pigment.  At the same time, pigment below the surface continues to be produced.  Where there is no pigment you see white.  Pied white can be patchy around the head and any portion of this pied effect crossing the eye will be seen as bull.   Sometimes you have two bull eyes while at other times it will be one normal colored eye with the other being bull.  Other times only a portion of the eye will be partially darkened by bull.  This is often refered to as a Cracked eye; an example shown below.  It all depends on where the boundaries of the pied affect occur as to which parts of the iris will show pigment.

When a bird is modified by the recessive white gene both eyes are bull.  Other forms of white such as grizzle white only effect pigment production in the feathers.  As such, grizzle does not have any effect on eye colors.  When you see a grizzle with bull or partial bull eyes, it is caused by the combination of both grizzle and pied white with the pied white being the cause of the bull effect.

The amount of light reflection is much less for the dark pigment and the only known pigment for the iris inner surface is dark for all pigeons.  Should there be blood vessels presence on the outer surface the red color is not as visible as it would have been on an orange or pearl iris background.  Nevertheless, under closes examination you can still see that these blood vessels are present.

Dr. Hoillander explained Bull eye this way "Bull eye is absence of granular pigment on the outer side of the iris; since the iris tissue is very thin, one can see the black pigment on the inner side.   Bull eye is commonly associated with white plumage and may be asymmetrical or patchy. "

Photo by RK Pair

Cracked eyes (partly colored or part bull) or eyes which are mismatched  one side colored and the other dark bull are always the result of no pigment present in the dark areas.  They are not a genetic eye color but rather the result of the same modifier that produces white feathers in piebald whites or splashed birds.   When skin and iris cells are coded for no pigment the skin (including the feather) and outer iris tissue do not produce their normal genetic pigments and white feathers or dark iris or iris spots are produced.

The two, white feather and dark iris, go hand in hand together.  You cannot breed piebald whites without the possibility of cracked or bull eyes.  However you can produce white feather by using grizzle and ash red that do have colored irises.  Neither ash red nor grizzle turns off iris pigments.  As such they have no effect on the eye color.  However since piebald does it will continue to do its thing in this combination.    So yes you can also combine piebald and ash red grizzle and still have the bull eyed effect.

In addation to bull eye there is another form of  dark eye that results from a mutation know as Dunkles Auge which is German for "dark eye" and given the symbol of "da"  This recessive autosomal mutation is epistatic to both pearl and orange eye colors. In other words even though a bird is geneticly an orange or a pearl; it's true genetic eye color is masked by this recessive dark eye gene and we see a very dark eye, much like that of a bull eye which results from pied white.  The Dark Eyes gene is not very common outside of the Arabian Trumpeter breed where it is most often found but it can be bred for if one has a bird that carries the mutation. 

Albino and Pink Eyed Dilutes

What about the pink eyes of albinos; is there a pink eye color gene?   Well NO, not in the same sense as orange or pearl.    The gene that produces pink eyes in albinos is the albino gene itself.    Albinos are devoid of all forms of pigment.  What happens is that the albino mutation interferes with the cells production of  tyrosinase, an enzyme which is a melanin precursor.  Without the tyrosinase enzyme there is no melanin production which in turn results in no pigment of any color being produced.    Pigment cells are still there but they are simply devoid of pigment.   In other words, the albino gene doesn't replace the pigment genes; but rather albino turns off the overall pigment process and results in no pigment anywhere in the body.   It’s this lack of pigment which causes both skin and feathers to be white; beak and toe nails to be ivory colored and the eyes to be pink. 

Ok fine, no pigment equals white but why the pink of the eyes?   Is this pink not a color and does it not requires some form of pink pigment?    The answer is simple enough; this pink is actually the reflection of blood in the eye tissue.  Blood carrying oxygen is red in color. As the light reflects through the eye tissue the viewer’s eye will see it as pink.

Here is a neat little experiment you can do.  In a darkened room, hold a flashlight up to one of the albino bird's eyes.  Point the other eye towards you and you will see your light as it passes from the first eye through the head and out the other side.  

Had there been pigment on the outer and inner surfaces of the iris, this light would not have shown through.  Had there been no pigment on the outer surface of the iris, with only the darker pigment of the inner side present, this darker pigment would be seen as a dark i.e. bull eye.  In the case of albino, there is no pigment in the eye period.  Light that passes through from one side to the other along with a small amount that is reflected off the blood vessels is seen as pink.  Thus pink eyed albinos and or pink eyed dilutes are not the result of pink pigments but rather results from no pigment being present in the eye.  I believe pink eyed dilutes are simply another form of albino but with only limited pigment being produced in the feathers but to be truthful with you the reader I have no information to say it is.  If anyone has more information on pink eyed dilutes please pass it along to me and I will up date the information here.

Other examples of eye colors

Let me repeat a statement I made above.  Today we find birds with other eye colors such as green, violet and even dark brown but proof that these are the result of additional iris pigment colors has yet to be demonstrated.  They may be new alleles to the known yellow and pearl forms or they may simply be modifiers to them as the Dark Eyed mutation is.  What we need is more data to learn the answers.  If you have such eye colors in your loft then I solicit your support by sending me up close photos of the eye like the ones you see here.   If you do not wish to study them, why not breed a youngster or two and give them to someone to study genetically for good data collection.



Green eyes from Stephen of India


The green eye on the right is from Jim Demro 

What follows are addational comments provided by Dr. Richard Cryberg.

Pigments in Rock Dove Eyes

Richard Cryberg

September 7, 2011


Feathers, in rock doves, have only three pigments as far as known today.  Those pigments are red, brown and black melanins.  Eyes in various species of animal often have melanins and in addition a variety of other pigments as well.  There is a lot of species to species variation.  Rock doves for instance have pigments called guanidines and pteridines in the iris of their eyes.  Yet, many species of doves do not have these two classes of pigments in their eyes.

First start with a general picture of the eye.  The eye is basically a ball shaped structure.  This ball has a hollow inside filled with a liquid.  On the back inside surface of the ball you find the retina.  This is for practical purposes an extension of the brain.  It has a considerable amount of data processing built right in the eye.  The purpose of the retina is to detect light and color but the built in image processing in the eye throws away well over 90% of the data collected and sends the processed and compressed file to the brain.

On the front of the eye there is a transparent opening we call the pupil.  This is where light enters.  On the inside front surface of the eye around the pupil and going back to the retina there are pigment granules that make the surface really black.  This black serves the same purpose as painting the inside of a camera black.  It stops internal reflections that could wreck the image on the retina.  More on this black pigment in a bit as there are things about it that are a real puzzle.

On the outside surface around the pupil there is a colored area called the iris.  The iris in pigeons ranges from a pink to greenish (rare) or blueish (rare) to orange to a whitish and any of these can have various amounts of blood vessels giving lots of tiny red lines.  Pink is what you get when you have no pigments at all and just see blood vessels.  The rest of the colors require pigments.

There are a variety of pigments found in the eyes of different species of animals.  Black and brown melanin pigments are quite common.  These are the main pigments found in human irises.  The rock dove has two pigments that are not often found in the iris.  One is called a guanidine and the other is called a pteridine.  That p on pteridine is silent.  Guanidines are whitish platelet like pigments.  They are very common in fish and give fish the silvery, shiny look  These pigments are quite opaque and stop light from getting through the iris.  Pteridines are an orange color.  Both guanidines and pteridines seem to be produced by pigment cells in the iris that look remarkably like regular melanocytes.  These pigment cells have dendrites just like melanocytes and sure look like another modified nerve cell.  It is entirely possible, I suppose, that these cells are just melanocytes and have a different compliment of genes turned on so make different pigments than the melanocytes that pigment feathers.  Of course it is also possible that ice in feathers is the result of some guanidine production by melanocytes.  So there is more than enough left to learn to keep us all happy with new ideas for a long time to come.

I can not find publications that show that the front part of the pigeon iris has melanin in it.  Still, I think that it is likely that there is some melanin in addition to the guanidine and pteridine.  It is hard to explain the greens and  blues and even hints of black seen in some pigeon irises if there is no melanin.  And clearly lots and lots of animals do make brown and black melanin in the iris.

When you have a normal bird with a mutation that shuts down production of the pteridine (orange) pigment in the iris you get a pearl eye.  In a pearl eyed bird you just have guanidine and perhaps traces of melanin plus the blood vessels.  We also know that a brown feathered bird has a false pearl eye.  Presumably the chemical that is needed to turn brown pigment into black pigment is also needed for some important step in the manufacture of pteridine pigments.  So a brown bird is unable to make pteridines.  This would be further confirmation that those cells that make the eye pigments are not all that different, and perhaps not different at all other than location, from the cells that pigment feathers.  Also, albino shuts off both production of guanidines and pteridines.  As albino is simply a mutation of the gene that codes for the enzyme tyrosinase it seems clear that tyrosinase must be important in production of both guanidines and pteridines.  This again would confirm that these pigment cells are quite close to the cells that pigment feathers.  I should point out that there is a significant difference in the iris of albino pigeons from various sources.  The Tumbler albino seems to have the best vision according to what people report.  Tumbler albinos are happy to nest at the top of the loft while some other albinos hardly are willing to leave the floor.  Looking at pictures there do seem to be some more or less white flat structures in the iris of Tumbler albinos that may help make the iris more opaque than other albinos.  It is possible that these structures are some type of guanidine and that not all albinos suppress guanidine production totally.  Or, they may be some unknown pigment type.

When guanidine production is shut down in an albino the iris is no longer opaque.  Some light is able to go right thru the iris to the inner eye.  This is likely a lot of the reason for poor vision in albinos.  Due to light entering the eye around the pupil it is not focused by the lens and there is a very poor image formed on the retina.  An albino of course is also unable to make the black pigment in the inner front surface of the eyeball.

I am not aware of any mutations that shut down the guanidine production and leave pteridine production intact.  I sure would not say it would be impossible to have this happen.  Perhaps we just have not recognized them?

Now, let us cycle back to that black pigment on the inner front surface of the eye.  In a recessive white or a pied bird with a white head the eye is called a bull eye.  It is basically black all over.  The iris is a bit different in color if you look real close but overall the impression is a black eye.  Pieds are often caused by failure of the pigment cells to migrate, just under the skin, to their proper locations.  Any area that ends up with no pigment cells has no pigment production capability.  If that place is the outer surface of the iris there are no guanidines nor pteridines produced.  The net result is with no guanidines which a great reflectors and a bit like putting lots of tiny mirror fragments in the iris you can now see right thru the iris to the pigment on the inside surface of the eye which is black.  So you get a bull eye.

The obvious question is how does this black pigment get on the inner front surface of the eyeball if pigment cells failed to migrate?  Well, it turns out that pigment cells have two migration routes.  One route is a surface route and involves migration just under the skin layer.  The second migration route is a core migration right thru the embryo's body.  This core migration seems to get pigment cells to the brain, intestinal tract, inner eye and a variety of other internal places.  There are even mutations that lead to black bones due to pigment cell migration into the bones.  I surmise that the pigment cells that work on the inner surface of the eyeball must be core migrants while those that work on the outer surface of the iris are just under the skin migrants.  Thus in a pied with a white head the just under the skin migration fails so no guanidine or pteridine pigments are in the iris.

Another great question is why is a bull eye always black?  Suppose I took a recessive red bird and added recessive white to it.  Would it not seem reasonable for the pigment on the inner eye to be red pigment resulting in something like a reddish bull eye?  Or the same game with a brown bird would lead to brown pigment in the inner surface?  Well, I do not understand the details of the biochemistry at all.  But pigment produced inside the body always seems to be black pigment.  It is easy enough to avoid red by simply not allowing any free cysteine around during pigment production.  And perhaps internally produced brown pigment is so dense it looks black?  So there are lots of  loose ends in this whole story that are not well understood.  Or at least I have not stumbled across papers that offer explanations.

Back to start page

Copyright 1999 by Ronald Huntley.
Permission is granted to download or copy
for non-commercial individual use only.
The author retains all other rights under copyright.

Ronald R. Huntley
Web Page Designer
Duncan SC 29334
phone: (864) 249-0276