The sparkle and rainbows given off by a piece of crystal are tied more to the quality of the crystal than the color. It is true that a clear crystal or a clear crystal with a simple coating will give you the best rainbows. However, the colored crystals are not diminished much at all. A lightly colored crystal like Light Sapphire or Rosaline will have a very similar effect to the clear crystal. Your may notice that the coloring of the rainbow is slightly off. A medium colored crystal like Sapphire, Light Siam, or Antique Green will have a greater tinge to the rainbow color, but still give off lots of rainbows. The dark crystals like Emerald, Dark Sapphire, and Amethyst will have a definite change to the rainbow quality. As the light is limited by the dark crystal color the rainbows do become less and the coloring is more noticeably off. If you have a specially colored crystal or one with a heavier coating, then you will get diminished rainbows. We're all about rainbows, so we don't normally carry the specialty crystals.