think of it this way, their chitin is not to different from crabs, lobsters, and other creatures of that type, so it's possible for them to have radically different colors. for my avatar, it's using my two favorite colors, but also, blue lobsters are something that dose happen in the wild, and as for the green, bio luminescent is commonly green. over all, if you look as the lobsters alone, the can have some crazy colors and patters, so that can easily be applied to the Lurkers.