The middle-dark color of the background is simply transp. red oxide with ultramarine, and it's as amazingly rich as it is simple - a deep nutty or smoky and inky brown depending on the ratio. (For all who are following, I finally have an Old Holland brand ultramarine which is very nice.) I notice that my camera flattens any bright red and orange, so some of the subtle transitions in such areas get lost in reproduction. For example, the passage here that looks like a single fat stroke of orange was definitely not this solid. I always used to hate when people say "the photo doesn't do it justice" but, alas, it's true.