I would like to mention they hail from the same home world that the elves originally came from. This being said they could easily share a common ancestry with elves and merely differ due to divergent evolution. This being said, their skin tones might simply mirror the variety that the elves possess, albeit with the addition of the colorful facial markings (and of course antennae). I mean it makes sense, they're also a race known for their beauty and being captivating even to other races, they have a deep respect for the balance of nature, and are gifted in magic (though psionic instead of arcane).
...Also they stepped in to take the elves' place as a player race...
As far as I'm concerned, in my games I will be treating them as if this was the case because it makes sense to me. For this reason I've also stated they all have elven ears as opposed to the humanesque ones they are depicted with.
Edit: Basically any normal elf skin tone, and as for the facial markings I'd say they run all colors.