HCA: Hermit Crab Association

I have orange isopods in my tank. I've had them for close to two years now. They've all been orange. But when I was cleaning my tank the other day I found a grey-black isopod! I'm curious if he's a genetic anomaly or if my orange isopods could lose their colour over a couple generations or what. Is there anything I should add to the tank to help them retain their bright orange colour?

It could be color morphs (not uncommon in isopods) or just one that shed it's skin recently.