Link on colored chicks.
From what I understand the dye is relatively harmless, but I personally feel that it takes away from the fact that it is an actual animal that needs care and attention, rather than a toy to be bored with and throw away after the feathers grow out, which contrary to the article I linked, takes longer than just a 'couple' of weeks to fully grow out.
ETA: I do feel differently about coloring chicks for scientific purposes, which has been done, and is more understandable to me.