This is a hard question since '
succulents' are a large variety of water-storing
plants, and 'tri-color' describes any of those
plants with three colors, usually green, white or cream, and pink or reddish. Can you tell us any more about what you have in mind? I have an aloe and a hoya, and Triss has a sedum that so far answer your question. I can think of some low, rosetting types, probably echiverias, or even some aeonium, that might suit. These
plants are very different, with very different growth styles. What are you thinking of?