Smokey is a partially or incomplete dominant gene. Heterozygous fish are known as smokey angels and have a typically light golden brown body colour with no obvious stripes. Whilst the rear of the body has darker mottled brown colouration often tending to black in the dorsal and anal fins.
Homozygous individuals the darker coverage is much more extensive and these are refered to as chocolate angelfish.
The fish in the photo above also carries a gold gene. It has been suggested that such individuals have a more golden appearence than individuals without a gold gene. This however remains to be proven.
Genetic code for a chocolate angelfish is Sm/Sm.