I have only found coloured carrots twice, both times at a Farmer's Market. The ones we got were a little sweeter than the regular ones ,and they made the chop so beautiful. I'd love to find them again.
I use the rainbow carrots in my chop quite often. I find them in a lot of grocery stores around me, so they aren't an odd find where I'm at. I started using them when I first got Chicken because she had a problem with the color orange for a while.