True Melanism

It seems in most animals, melanistic (specifically hypermelanistic) refers to an animal which is purely black, with little to no pattern expressed, yet in ball pythons melanistic does not seem to mean that. Ultramelanistic animals appear to be lighter than some normal ball pythons, and the closest thing you get to pure black as far as I can tell is 8-ball, or other black pastel variations. In other animals it seems that melanism is a singular mutation that overrides all other genetics that dictate coloration and/or paterns, but with ball pythons it seems that the melanistic look is only produced by combining multiple mutations, and the result is clearly different. I am very ignorant when it comes to how the genetics work in these animals, so I would greatly appreciate if someone could explain this. Is it possible that there could exist a ball python that exhibits melanism in the same way as other animals that has just yet to be discovered? Thank you for any and all help.