I've blocked in the background and worked on the ground. The colors of the building may change as I get into the horses, but I don't want to mess with it too much at this point. My thought is to keep the horse shadows warm, but I might find the need to adjust them cooler once I have the main subjects painted.
Inside this building is the Horse Guard Museum. It is well worth the visit if you are there to see the changing of the Horse Guards.