GRAY OPAL A solid Opal which is opaque or translucent showing a play of color on a gray base. Determined by looking through the top of the Opal beyond the play of color. If the shape is appealing to you - go for it. Opals must have inclusions in order to have color. Avoid gray, cotton or white areas that are dull and show no color.
Color is almost everything in Opals.
The more color the better. Reds, pink, yellow and orange are harder to find, and therefore are more expensive. Green, blue and violet are much more prevalent. No one pattern is more expensive than another. It's the amount of color and its intensity that makes it better than another.