However, according to this resource (don't know how accurate it is, but it doesn't ring any alarm bells) [
http://www.marbledcrayfish.com/experiments, the blue color is only temporary while you're feeding color enhancing foods. So, while you may get a blue marbled cray, if you stop feeding it those foods, it MAY revert back to its original brown coloration.
PS, in no way do I condone releasing these into the wild, even though the resource's author mentions he doesn't think it'd be a bad thing. However, for an aquaponics system, well, I'll have to think about that one lol