Lots of fish come in different colors. Often the male looks brighter or more colorful then the female. Also young ones look different, they change color and shape when they grow older.
But why do adults change their color? Mostly is to blend in with their environment or to send a signal. The brightest, most conspicuous pattern are used in mating season or to show aggression, or to defend territory. When the fish pales or shows stripes or other patterns it is usually a form of camouflage. Sometimes activity or mood shifts can change the color. Some fish change color at night, making them almost impossible to identify. Red is a good camouflage for night active fish. And sometimes it is just not known.
Young tiger grouper have contrasting black and white bars. The adult can rapidly change between dark (aggressive) and light. On cleaning station they turn reddish.
The normal color of the coney is solid tan to reddish brown. The bicolor phase is mostly seen in the morning or later afternoon when they are hunting or are excited. Resting they show a blotched pattern. The golden coney is probably a result of a recessive gene.