Depending on how long they have been there, could be 50 years or more (at least 100 or more generations)(I had Hemichromis guttatus, back in the late 1950s), whatever color variations were best suited to that environment, may have been favored over that time.
They look like normal guttatus to me.
There are feral populations in Cuatro Cienegas Mexico, and even feral populations in certain warm springs in Europe, released before people were aware of the damage feral species can do.