unusual coloration of species…

[Magnum Man75 189]

there are several fish that seem to show local color variations, within the same species…
this potential, is evident to me daily, in our local squirrel population… which is predominantly grey squirrels… several years ago, we started seeing occasional black ones, now years later the black ones are taking over this area…

it’s not hard for me to imagine this happening in specific locations with highly colorful fish… thoughts???

 

[GaryE35 33]

No need to imagine. There are tons of examples in the hobby. Sometimes the colour differences can be really striking.
The flip side is cryptic species, where you find find two seemingly identical fish in two different places, but when DNA is done, they aren't the same species. It's just that the genetic changes that cause them to be different species don't affect what the limited human eye can see.
There are fish that don't travel a lot that get cut off from each other by habitat changes, rivers rerouting, ridges rising and all the things that happen to land and water over great amounts of time, and that change patterns with changing fundamental DNA. They can still interbreed easily, but they look really different.

Here's a fish I love, Aphyosemion elberti, a killie. All the forms pictured never meet in nature and are isolated from each other. But they breed true - the young look like the parents, and not like the other forms.

 

[Rusty_Shackleford74 189]

There are fish that don't travel a lot that get cut off from each other by habitat changes, rivers rerouting, ridges rising and all the things that happen to land and water over great amounts of time, and that change patterns with changing fundamental DNA. They can still interbreed easily, but they look really different.

This is exactly what happened with Mbuna from Lake Malawi. They all originated from a single Haplochromines. Population on rock group A are separated from rock group B by an open sandy area. Crossing the sand area leaves them open to predation as well as having no rocks to feed on. Populations rarely mix and eventually become a separate species. This is happening at such a fast rate ichthyologists are actually able to see new species evolving in front of their eyes.
This is also happening with species of dart frogs. They are separated by a geographic element be it a river or mountain range. They develop color morphs. One one side of the river a frog may be blue with yellow spots, on the other side green with blue spots, but both are the same species. At least for now.
Both examples show why it's important to locales as different species and keeping them separated in order to keep the lines true.

 

[emeraldking54 105]

it’s not hard for me to imagine this happening in specific locations with highly colorful fish… thoughts???

With livebearers, it's the same. Depending on the location in free nature the same species can be different colored or even patterned. There are several factors in play why there are different color morphs. Most are external factors besides genetics.