To me (and I'll admit that my eyesight isn't the best) it looks like it could be the lighting that gives them the color tones, rather than dye. I have seen photos of dyed axoltls, as well as fish and Xenopus, and the colors of dyed specimens are usually much brighter.
Regardless, I am opposed to the practice. Animals are dyed to make them more attractive, so they can be sold as toys to children and others that probably shouldn't have them.