Seelie being light and Unseelie being dark.
Such as the light and dark courts of the Fae.
*Fay, Fey also means it but it's rarely used nowadays.
Faerie are an entirely different species often mistaken as or for Faries.
Sorry, couldn't resist clarifying, I'm a fairy nerd.
Unseelie, however, means evil fairy, which is a definition trying to be avoided.
I saw the name Crystal earlier, which from my perspective, seems a bit misleading.
As amazing is it would be to have Crystal specials, we do not, we have "Albinos", and they are not designed to look crystal like.
Now for suggestions:
How about Albus or Albi for Albinos? Albus means white in latin, and it'll remain somewhat similar to the original, but with a meaning that's being aimed for.
As for melans, what about Ilunistic instead of Melanistic? Ilun means "dark" in Basque.