The Gakuran Roblox hair options I found are black and gray. One source lists Gaku Hair in black and Gaku Hair in gray, which matches the most common color variants seen for that item.

Hair colors

  • Black.
  • Gray.

Extra note

There are also other Gaku-related accessory items around the same set, but for hair specifically, the clearest colors listed are black and gray.

TL;DR: Gakuran Roblox hair is mainly black and gray.