But native mudokons are green to start with, so the chemicals would have to alter their colors differently, which has never happened to my knowledge. When it comes to Abe's being blue, I think his color is a symbol, showing us that he is different from all other mudokons (since he's the savior and all, plus he has the sole weilder of that nifty Shrykull ability
). That's all that I can really think of, at any rate.