Honestly, I don't see the harm in a little non-toxic dye. As other posts indicate, some of us have dyed other things (pets) now and again. I don't think it's horribly cruel, certainly better than other things like caponizing or battery cages. It's just a little dye that comes off, if it brings new people into the chicken world (which it does) so much the better. People impulse buy all the time, I don't think it matters if the chicks are pink, blue, green, or "naturally" colored. Last year I decided I wasn't going to buy from the feed store, so I placed hatchery orders. I was swimming in chicks already, but the first time I went to the feed store, what did I do? I bought more chicks. On impulse. Yes, an on impulse. It happens.
Be the chicks colored or not colored *some* people will learn about their care and *some* won't. You won't change that, even if chicks aren't ever allowed within fifty feet of a little blue food-coloring.