Skin colour? Nowt to do with the force m8. Maul is a Dathomirian Zabrak the males are Red/Orange/Yellow, females are Blue/Grey/White/Tan (although that's probably problematic under Disney) - the witch you are referring to is just a bog standard Zabrak by the look of it
Ah I didn't know I just assumed they got bright red and black when they go to the dark side..I could have sworn in a game or Intro for the old republic I saw female version of Darth Maul.
Ah wait just checked same colours as Maul but she was a different race.