I'm no stranger to doing very questionable practices when it comes to knitting. Combining yarns together because I got a really good price on a size that is too small is normally the culprit. When the colors of the yarn are all the same you don't see the inconsistencies of knitting, like one yarn favoring the front or back side, or one yarn may not even catch a needle. Once you mix different colored yarn together the issues become very obvious.
See what happens when you run 2 ends of yarn in parallel, wind/double it, and then twist it. Which do you prefer?
