The fact that this animal is a rescue and looks to be very malnourished it could be suffering from hormone imbalances due to stress & poor diet that have affected its color.
From those pictures it just looks like a normal under some odd lighting.
I have a snake that too lacks any black on her body (like the snake in my display pic), and has been this way for years, but in her case I haven't proven if its genetic yet.
so just feed that snake back up to health and see if its colors become more vibrant.