Coal dust. It's not skin, it's coating. "But she's royal, not in the dust!", ah yes, but standards of beauty are that the hardest working, strongest, most results-creating dwarves get the most coal-tarred, and so the royalty artificially has it put on, as they clearly as the most strong and hard-working of all dwarves.
Now, BROWN skin, that one is harder... The best I can do is this: Dwarves are, by lore, formed not from flesh and soul like Man or Elf, but from rock. Various rocks come in various colors, and so a mudstone or mica-originating dwarf would have brown hues, while a granite-based one could be red, grey-white, or even blue.
Plus how the hell does a subterranean race develop black skin?
Black-skinned subterranean:
Coal dust. It's not skin, it's coating. "But she's royal, not in the dust!", ah yes, but standards of beauty are that the hardest working, strongest, most results-creating dwarves get the most coal-tarred, and so the royalty artificially has it put on, as they clearly as the most strong and hard-working of all dwarves.
Now, BROWN skin, that one is harder... The best I can do is this: Dwarves are, by lore, formed not from flesh and soul like Man or Elf, but from rock. Various rocks come in various colors, and so a mudstone or mica-originating dwarf would have brown hues, while a granite-based one could be red, grey-white, or even blue.