Minecraft wiki entry for Tropical_Fish, associated text: When tropical fish spawn in the wild, 90% of the time they appear as one of the 22 varieties seen on the right, and the other 10% of the time their patterns, size, and colors are completely random, drawn from any of 2 shapes, 6 patterns, 15 base colors, and 15 pattern colors. The color black does not appear on any naturally-spawned tropical fish, since the eyes are usually hard to see.[2] These result in 2,700 naturally-occurring combinations.