Agree with Jexnell, there are 9 different species in the genus Thorichthys, and most LFSs can't tell the differenence one from the other, so might call any of the 9, FMs.
And even within the species meeki (the standard fish thought of as a fire mouth) there are location variants that will have different colors one river or lake to the other.
An individual from Rio Candelaria might have much more red than one from Laguna Bacalar (the Bacalar variant seems to have replaced the red with yellow), or an individual from Roaring Creek in Belize may have much more blue spangling. It all depends on where the original ancestors were caught.
It also may depend on what color works in a certain habitat. What predators are able to see and weed out, under certain water conditions like turbidity, or how the substrate effects predation, and if another color variant gets away, those are the genes that are passed on.
There is also the tank breeding factor, where that survival of the fittest isn't a factor, and certain colors get washed out, when too many of a spawn are allowed to live and reproduce. In nature only the best adapted, and the most attractive to the opposite sex get to reproduce.
Below a Chuco intermedium from one river.

now below another Chuco intermedium, from a different river system
