"Dusky Blue Fawn" is sort of an oxymoron. There's a Blue Fawn (wild-type grey mallard pattern + a single blue dilution), or a Blue Dusky (the dusky blocks most of the wild-type grey pattern - so, it eliminates the white neck ring and claret breast, etc., and if you add a blue dilution on top of that, you get a Blue Dusky...)
This is a juvenile Blue Dusky Runner hen - I was working on this color pattern a few years ago, but got out of them to focus on Magpie Call ducks instead:
