What kind of soil you got there? It has a great impact on fish color. Have you ever seen the same fish sort caught in swamp pond and in a really clear lake? The first will be really dark.

But probably high water temperature may affect the color also. This weekend I was fishing roach (dunno whether you know such fish but it doesn't matter anyway). Normally they got orange fins but my fish were pale - really pale. Usually they get pale after being dead for some time. Probably that's because of warm water there...