Might want to contact ideal directly to get the info, I belive they have posted before about it and it was a food coloring after hatch via spray or something. I think there are some smaller hatcheries that also dye, but can't think of them at the moment.
Let's be careful now and not get into the dye or not dye issue on the chicks as it has been a hot topic in the past. There are always both the good and bad examles of their fates so we should try not to get carried away and instead educate those who end up with chicks. General concensus from my memmory is that many do not like it and it encourages illresponsible ownership, however, it gives "extra roos" a chance to have a life, instead of being euthanized right away. Not all dyed chicks are extras though.