All Viera having white hair was actually a quirk of lore added in FFXII! In Tactics Advance where the race was first introduced, pure white hair was actually a rarity and most Viera had hair in shades of light pastel tones like green or blue. Incidentally, that's why my character has pastel pink hair.

In FFXII, it was common for urban Viera to dye their hair to fit in better with Humes. There's a couple NPCs in the intro cutscene who have dyed brown hair. Interestingly, their ears are also brown. What I wanna know is whether those were dyed as well, or if they just had naturally brown ears to begin with.