However, matching two or more different gems is not something one can do blindly and expect great results. For instance, a blue diamond three stone ring that has brown topaz set beside the center stone would not look too good.
Pick colors at opposite ends of the spectrum. They can balance each other visually and deliver a stunning look as long as you are careful about the sizes and cuts you choose.
One dominant color alongside another, more muted one, can be a beautiful thing to behold, especially with gemstones.
Matched colors that are essentially the same but in different shades, can be appealing to the eye. All yellow, for instance, means you can go with Yellow Diamond, Yellow Sapphire, and Citrine.
Three or more colors on a color wheel that are equally space from each other are a good option. While these can be a bit hard to balance, you can pull it off if you let one of them dominate.