Changing Color Drink (for parties, just to look cool)

  It would be nice to have a liquid drink that changes color throughout the night. The air temperature would gradualy and slightly heat the glass causing the liquid inside to change color.
  Problem is would it be safe to drink such a drink. If not just reverse the effect. Have a liquid inside two thin layers of glass inside the glass and the temperature (of the drink) inside the glass changes the outside color. Have a light imbeded in the bottom of the cup to enhance the effect.