I'm trying to remember a movie I saw on TV in the mid to late 90s. It was live action and probably on the Disney Channel or Nickelodeon. It involved a strange teenage girl who was gradually revealed to be an alien. I remember a scene where an adult woman asks a man who is some sort of alien expert if teleportation is possible. He says, "Like Star Trek?" And she replies, "Like that, but purple." I believe the girl might have been a twin, and also that there were horses involved. Does this ring any bells for anyone?
I believe you are thinking of the 1990's reboot movie of Escape to Witch Mountain.
When they use their powers, they are shown as purple.