Anyway, this is what it says in New Scientist.....
I wonder whether any New Scientist readers can shed light on an enigma which has been perplexing my daughter and myself. Why aren't sheep green?
S.P. Kingsley
(31 August 1991
I believe the answer may be this: sheep are most at risk from predators when alone rather than when congregated in a flock. They are most likely to be isolated during the winter months when they are often caught in snowdrifts. Under such conditions the white fleecy coat would have two advantages, warmth and camouflage. Such sheep would have an evolutionary advantage.
Elaine Dignan
(14 September 1991)
Sheep are white so that they blend in with a natural limestone scenery (eg the Yorkshire Dales). A white (or grey) sheep blends in perfectly with a rocky background, whilst it looks more like a small rocky outcrop when against a green background. Often a walker not used to the higher altitudes and camouflaged sheep will stand on a 'rock' and find it moving quickly from underneath him. The walker usually ends up feeling rather sheepish after such an encounter.
Richard Marsden
(14 Spetember 1991)
It is evident that the lack of greenness amongst sheep has evolved as a defence mechanism against ducks - sheep being permanently quadrupedal, they are four times more likely than a flamingo to be bumped into by ducks. If green sheep ever evolved, they would suffer substantially greater inconvenience as they would be invisible against a background of duck-weed, thus provoking even more collisions.
Tony Howard
(14 September 1991)
Perhaps there are green sheep, but no one ever noticed.
Adrian Bowyer
(14 September 1991)
Recently, Stephen Young showed that whereas lowlier aquatic animals like hydra do have green symbiotic algae, there are no green herbivorous mammals or other terrestrial animals because they have such a small surface area compared with that of plant leaves that they could never photosynthsise a square meal
Michael Cotteril
(14 September 1991)
All the familiar breeds of sheep that we see today are the product of artificial selection created by generations of farmers, and they have probably been bred for white wool because it will take up dye more easily and is therefore more valuable.
Carole Nadin
(14 September 1991)
All your writers about green sheep assumed that all mammals use their senses in the same way as humans. The primates are the only mammals that can see in colour; the others see in black and white. I a black and white photograph, green and grey are the same shade. As most mammalian predators hunt by scent until they are very close to their prey, the question should have been; "Why don't sheep smell like grass?"
Derek Mayall
(28 September 1991)
PS To a bull, the matador's cape looks dark grey.