I was lucky enough to catch one of my crayfish molting. Pictures show before and after. I had been feeding them algae wafers and switched to bottom pellets. I think thats what made the color change. I try different foods to get different colors. I have some that have bright blue and bright red mixed on them. This tank is a 65 gallon tank with all sand,rock, driftwood from the river. I even pulled the brick out of the river when I was kayak fishing and added it to my tank.