I've recently been doing very well on egg sucking leeches/ black wooly buggers through tail ends of current/riffles right before the holes. Pink eggs or red eggs on the leeches. No weight. Stingy fish know when something is not drifting naturally. Cast farther up the riffle to drop your flies to the depth you prefer.

I would try a pheasant tail or hairs ear nymph. You could also try a mikey fin.

Black has been mentioned, and it is effective, but white is also very effective. It appears white, for some reason, is effective in cold water. For one thing it is very visible. The white biots used on Prince Nymphs make this fly very effective in the Winter time. I use white woolly buggers dead drifted through the slow holes, or slowly stripped, and have had very good results. A trout is cold blooded, and their metabolism slows when the water turns cold thus you find them in slow water.

Egg sucking leech is where its at. Black with red has worked really well with me.