Pearls are available in a variety of colors. White, cream, golden, pink, silver, gray, blue, green, and purple are the most available of the saltwater variety. Freshwater also are available in pastels.
Lustre of a good quality pearl should be bright, not dull, enabling you to see your own reflection clearly on the surface of a pearl.
The surface varies with any treasure from nature. The fewer blemishes, like spots, bumps and cracks, the more valuable the pearl will be.
The shape of cultured pearls also varies, the rounder the pearl the more valuable it is. However, fashion dictates trends.