My toads are turning black!!!

[DDskary]

I am more of a hobbyist terrarium builder but within the past year or so i decided to start putting live animals in them. I have been using non-toxic and safe food coloring to apply fake blue tones to the water. I've noticed after cleaning my tank (once per month about) and adding the coloring that by the next day one frog remains normal color, the other becomes dark or black, AND the shade of the water is considerably less blue, thus leading me to believe that he is absorbing the food coloring. Not that you would be using food coloring in your setup, but the fact that one or more is changing to a darker color could indicate he is absorbing something from the water/environment, OR that he is simply under stress. after a couple days his color usually returns to normal and i can add more food coloring without any change to his color or the water, indicating to me his stress levels have lowered and he is calmer in his surroundings. If the tank is cleaned and no coloring is added to the water, he still becomes darker, leading me to believe that it is almost entirely stress related, which may be brought on by the fresh, yet de-chlorinated, water being replaced, though it does not seem to happen when only adding water to the existing water.

[elliotulysses]

From what I know, it's not uncommon for fbts to have some color differences. In my tank of four about three of them are really bright, but one is definitely darker(not black like others have mentioned), but his belly is very bright and he's one active dude; he will lunge from across the tank when I get out the feeding tongs. While I am far from an expert, I think that behavior, eating, and belly color might be more important. My little girl that had an impaction was very bright green, but her belly was faded and she was super lethargic/would not eat. Sadly, she passed, but IME those things are more concerning than just her back color. From what I've heard ftbs can even come in a brown shade, so who knows?

[japa]

Colour change (turnig dark)is normal for FBTs. It is about nervous and hormonal basis.
This is a complex process which plays a role Intermedin hormone concentration in the blood. Most bellied darken only a couple of days, about a week or 14 days, so you do not have any concerns.