In some environments (think of the Faerunian Underdark for a fantasy example, or a planet orbiting a pulsar for sci-fi folks), high-energy (UV and up, but I'm mostly concerned about UV and very soft X-rays here as hard gammas are going to make animal life impossible anyway) radiation predominates over visible light in the environment in question.
Assuming that other issues (food chain is solvable, see this answer for details)) are taken care of, would terrestrial animal (or better yet, sapient) life in that environment evolve melanism (i.e. very dark skin) as a result of the radiation-heavy environs? Or would this be counterproductive as an evolutionary adaptation? Am I already talking about a point where the environment is too radiation-rich for even a basic lizard to evolve, never mind intelligent, terrestrial life? (Oceanic life has it easier as water is a pretty good radiation shield, so I'm putting it out of scope for this question.)