Murder (said old Quong)—oblige me by passing my pipe—murder is one of the simplest thing in the world to do. Killing a man is a much simpler matter than killing a duck. Not always so safe, perhaps, simpler. But to certain gifted people it is both simple and entirely safe. Many minds of finer complexion than my own have discolored themselves in seeking to name the identity of the author of those wholesale murders which took place last year.
What exactly does discolored themselves means in this novel of The Hands of Mr. Ottermole by Thomas Burke?