I believe only Saurians and Aliens can be purple. All other races have normal skin tone or Blue, Green or White, but no Purple. Fortunately any rarity of Saurian or Alien can have purple skin.
If you don't care about race, you can get Very Rare BO off the exchange. Sometimes very cheaply if you aren't picky. Rare & Very Rare Gorn are Identicle once you start swaping skills on them.
But Be Careful, Season 4 has messed up the rarity sort on the exchange, at least for BO. So make sure it has 2 Superior traits before purchasing (Except for Gorn who only get 1 Superior trait and always have Basic Reptilian strength)