The Scientific Anglers Mastery Steelhead line is an ideal choice nymphing needs on big water and has ultimate line control at distance.
SA has built their Steelhead line on a braided multifilament core, with low stiffness, which allows for moderate delivery in any fishing condtion. Because of its unique taper both front and rear it allows you to cover a ton of water. The longer head will help with increased shooting distance and the rear taper gives superior mending and roll casting out to 70 feet; which both are key elements for big water.
This line will stay supple in very cold water and will turn over very large flies even at distance.
As for color the Scientific Anglers Mastery Steelhead line comes in Mist Green and remains visable at distance and comes in line weights from 6wt to 10wt.
The cost of this line like most Mastery Series lines is $69.95