When fishing spring creeks where the water is gin clear I like to color up the first 15 feet or so of my fly line with a black art marker from hobby lobby. costs around 5 bucks and will last for about a season of heavy use.
I also carry a black art marker with me on stream to tone down colors of my dry flies. And they work great to add eyes, body markings, etc. to foam body flies.

Bubba