It appears to me that the hypermelanistic chams are missing pigment in certain areas of skin that do not allow them to change colors, or remain only dark shades such as brown. Is this this case? If so then it would seem this is another genetic defect. Kinda neat, but if a defect, i would not support the production of them. However if it is simply a randomly generated trait, i would find it very interesting to be able to own one. By randomly generated, i mean randomly generated such as the white bear, or the true-yellow eyed tree/clown frog ( i cant remember the exact name, maybe someone can help me out. )
In anycase, there's my 2 cents!
have a nice day.
-Marc