The mustard gas betta is an absolutely stunning form of the betta fish. These fish are bi-colored or, in some cases, multi-colored bettas, having different colored fins and bodies. The fish’s body is typically dark in color, usually blue or green. The flowing finnage is usually orange or yellow, with the color spreading outward from the body in cloud-like waves, hence the variety’s name. Sometimes, the variety is incorrectly referred to as chocolate, as the fin color is similar.