I fish a very small creek, average width is 18 inches, but it is relatively deep, 3 ft in spots. It is overgrown with grass and houses both brooks and bows. Both species from this creek tend to see little direct sunlight and are very dark in comparison to the more normal colored trout. This tends to support Lunker's comments.

Tim

PS: Do an advanced Google search, subject: Fish coloration. This might prove helpful.