You should be matching up dye lot numbers and/or dates on the yarn wrappers in order to try to make sure that ALL skeins/balls of that particular color will match up with each other. Even the skeins of "no dye lot" yarn usually have some kind of numbers and/or dates on them that you can and should use to try to match up especially if you are planning on using more than one skein to make an item. You should also look at all of the yarn you want to purchase under a bright light/sunlight to visually inspect and compare each skein of yarn to the other to make sure the colors match up and there isn't a noticeable color difference between/from one skein to the next. (Please note the key word "try" in my first sentence of this paragraph!)
Just because a yarn has no dye lot, it does not necessarily make it a perfect color match from one shopping trip to the next - you should try to purchase all the yarn you need for making your item on the same day and, preferably, in the same store so that you can try to get all the same color of yarn from the one same shipment/batch.
Some of the yarn companies don't use "lot numbers" on their so-called "no dye lot" yarns but they do use dates or date numbers. I haven't asked anyone but I think they do that because they need to be able to keep track of the yarn that's processed/sold in case of any problems or recalls with a certain batch or type of yarn. Look carefully at each yarn wrapper and try to match up the information on it in the area where you would usually find a lot number/batch number/date with the yarn you're planning on buying and be sure to look at each skein to make sure the color(s) match from one skein to the next.
In my own experience of 40+ years as a knitter and crocheter, it does not matter what brand/type of yarn is used - color(s) can and do change from one batch/dye to the next. I don't think the yarn companies have that part perfected as of yet - as long as people/humans are involved in the process, I don't think they can make it perfect because there is always allowance for human error(s).
If the yarn has a dye lot number on it or some dates/number(s) on the wrapper, you should try to get the same type/brand of yarn and match up whatever the numbers or dates are on the wrapper with other skeins that you buy as all batches of yarn can vary from one batch to the next. If you know in advance that you can't get enough yarn in a particular batch/dye lot #, you can always try alternating (mix & match) the skeins from the different batches/dyes but I think it would depend on how noticeable the color change(s) are between the skeins as to what to do with them and it would also depend on the item you want to make. For example, the color changes would probably not be as noticeable in a striped afghan or sweater compared to a solid color afghan or sweater.
If you are having trouble getting enough skeins of matching colors of yarn, you may want to ask the store where you do your yarn shopping/purchasing if they can special order some for you as I know there are quite a few stores who are willing to do that upon request including Hobby Lobby but, by the same token, there are probably at least a few stores who aren't willing to do that. I know that if it were me and the store couldn't or wouldn't order the yarn for me, I'd be shopping elsewhere and probably wouldn't be going back to that store again for future yarn/craft purchases. I'd probably let them know the reason why, too!
On 23 March 2006, after reading (and participating in!) some dye lot/no dye lot yarn discussions in a couple of crochet groups that I'm in, I decided to send an e-mail to Caron that said this: "I would like to know what the purpose is to having some yarns with "no dye lot" numbers on them. The colors do NOT always match from one color batch of yarn to the next and without the dye lot numbers on them, it can be hard to match up the colors without a very noticeable difference from one purchase to the next."
Here's Caron's response to my e-mail which I received on 24 March 2006 and I changed the font color to blue for the copy of their reply:
"You have a really good point.
The concept of "no dye lot" yarns works great, as long as you can rely on fiber suppliers. Acrylic yarn is an indirect product of petroleum. The cost of oil the last two years has driven major fiber suppliers out of business. This has forced us to search for new suppliers and created a difference in the shades on some colors.
We regret the inconvenience to our customers but it is circumstances beyond our control.
The "no dye lot" yarns are dyed in very large batches (10,000 pounds) and most of the time a customer would get the same color.
We now have a new supplier and the shades should be consistent in the future.
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