Well I guess I will elaborate on my previous simple post....
I fish stillwater, I mostly use the black colored beads, Because they look more natural than a gold ball at the front of your nymph. Sometimes though, I use gold or silver beads on my nymphs because I want the attraction( Dingy water, tough days etc..)

And since I fish stillwater the fish can take their sweet time to decide whether or not they want the fly I'm presenting to them....It's not like in a small stream where the fish will pounce on a lot of things because that might be there only chance to eat that day.