Sherlock Holmes had dark brown wings. They often looked black, but showed their true color in the sunlight. Dark brown was close to black, and understandably made the few people who could see wings a bit skittish. Not that he needed help in that department; his personality drew that reaction from a great many people by itself. But everyone who knew about wings was aware that black was a bit Not Good.
Not many people were born with the ability to see other people's wings, an estimated "less than 0.01% of the population." Mycroft, of course, was one of those people; Sherlock had to be taught. The ones who could see wings often didn't speak of it—those who did were deemed mentally unstable by their blind peers or put in some sort of therapy or mental institution. Sherlock had learned long ago not to talk about wings.
He sometimes dreamed about flying. His wings would catch the air and fling him into the sky, up and away from the world. But wings weren't tangible, however much he wished them into proper existence. Sherlock couldn't fly.
His dark, stiff plumage had always covered a layer of downy white feathers that only occasionally peeked through to greet the sun. But then he met John Hamish Watson. John Watson, who made tea and killed a man for Sherlock. John Watson, whose tan wings almost matched that cable-knit jumper of which he was so fond. John Watson, whose hands pulled triggers and stitched wounds equally well. John Watson, who called him brilliant and amazing and honestly meant every word of it. Sherlock found more white—proper feathers, not just fluff—and wondered how much John had changed him and if he should be worried about it. He decided that he might as well give the man a chance.
He taught John how to see wings, how to squint your eyes and look at them sideways, just so. It was easier with practice, and Sherlock noticed him practicing constantly. He taught John what the different colors of plumage meant about the person, but not all of the colors—no need for John to know about his. He taught John that it was easier to tell if someone was lying by watching the way they held their wings instead of searching for minute physical tells. The greater portion of the population was unaware that they even had wings, so they could hardly practice controlling this other form of expression. He didn't find himself caring so much that John could tell what he was feeling: he had been able to do that even before he had been able to see Sherlock's wings.
"Falling is just like flying…with a more permanent destination."
"Goodbye, John." He spread his wings wide. Since when had they been white? It didn't matter anymore. Sherlock took a step forward and fell.