In order to find the Easter egg, drivers must engage the autopilot system by pulling the cruise control stalk towards them. Once autopilot is activated and a blue icon is illuminated, drivers need to pull back on the cruise control stalk four times rapidly. When this occurs, the typically grey road representation in the dashboard turns into a psychedelic cowbell road that is reminiscent of the "Rainbow Road" map in Mario Kart 64.
While this particular Easter egg isn't too exciting, previous gags have included turning the Model S in to the Lotus submarine from The Spy Who Loved Me and showing a wrap speed montage on models in Ludicrous speed mode.
Speaking of the Model S, Tesla just unveiled the facelifted variant yesterday. It features a modestly revised exterior with a new front fascia and standard LED headlights. The Model S also gains several new interior options including heated / ventilated front seats, a medical-grade HEPA air filter, and Dark Ash or Figured Ash wood trim.