A cyber friend from another board who is fully capable of tying a perfect size 20 Parachute Adams ties the scruffiest flies for himself you'll ever see. He has been experimenting the last few years mixing the bright colors you're talking about into regular patterns. Well, regular for him. He ties these scruffy nymphs with lots of UV and florescent duns mixed in. He catches a lot of fish and says the addition of bright and UV colors has seemed to up his already better than most catches.

And soaking your flies in liquid power scent overnight will do wonders too.