That's the case with all fish with markings. And all fish are darker on the back in clear water, with more vivid colours especially the primary colours.
p.s What's with all the gloves, you little benders
well a few are stocked but any under 4 lbs are wild but they are cracking sport and are quite a challenge to catch.
Did you use a dry or a nymph or a worm? even a 3lb Brown is a large river specimen now a days.