I have been keeping two matas for the past 2 years. In that time I have noticed a big change in their shell coloration. Their shells have gone from the healthy dark brown I am accustomed to seeing to a light beige color. It simply doesnt look healthy to me although the do not have any shell rot and seem to shed their scutes without trouble. Their tank does not get direct sunlight and I never turn the flourecent lights on in there. Could it be a light/pigment issue? Unfortunately their diet doesnt vary much- pretty much all fatheads or rosys depending on whats available. They are very fiesty so I only get vitamins into them every month or so. Could it be a malnutrition issue?