No worries. If this is your first rodeo w/ BTAs they're pretty hardy critters - The only color change I'd be concerned with would be white (or translucent). Bleaching is a bummer. Your BTA's mouth looks closed. I'd probably just let it sit on that rock and do BTA things.
Here are 5 pictures of my BTAs (all clones of the same daughter) through the years under different lighting and different levels of happiness over the years. Their colors will change under different lights IME. I notice a difference in color and depth during the lights cycle/time of day as well.
I'm not a photographer and these were all pretty much taken under "default" type phone camera settings.