The shimmering colors that appear on an opal are a result of the composition of the material. Light refracts off the tiny, closely packed spheres of silica inside the stone. The larger and more ordered the spheres of silica are, the more intense and varied the colors. This effect in opals is called 'play-of-color'. All colors are not equal and some are valued more highly than others; red more than blue, for example. We recently began stocking white opal in rose cut form, and it's a fantastic cut for this material, really emphasizing the shimmering colors. This is Ethiopian material, which has a high water content, and which has a distinctive play-of-color that appears to hang suspended within the stone.