I’ve read that blue can be a very powerful color for flies in the winter.
Last year, I tied up various nymphs to incorporate the color. Sometimes, the flies worked not at all. Other days, they pulled in fish after fish.
On one memorable February day, I was fishing in a snow storm. All of my takes were via a #20 midge larva, like the one above. Sometimes, the fish took the dropper, and, sometimes, they took the anchor. But, when I switched away from the midge-with-blue, all takes stopped. They ignored the new dropper and the old anchor.
I remembered that day as I this morning went through my fishing journal. I have long forgotten about that midge. But, today, I’ve tied up a half dozen to get ready for February.
Click here for Ed Engle’s thoughts on blue flies. It is in one of his books, Tying Small Flies, that I read about nymphing with blue midges. I’ve read all of his books, and I attended his nymphing seminar at the 2016 Fly Fishing Show. That man is a genius.
Below is a blue fly from Tightline Productions. It might be the one referenced in one comment below.