Here are the two chips in my collection. I am betting the base color of the chip is pink and the maker put blue over it to make it a blue chip. It doesn't take much table wear to let some of the pink show through.

It's always possible there's another explanation. Another 2.50 collector gave me the one on the left but I don't recall what he told me any more. Maybe Peter is reading this; that's probably where the first chip came from a few years ago.