I began work today by making the burnt sienna and burnt umber stronger, brushing on the color with vertical strokes of the brush. Above the brown, I painted strokes of cadmium red light, cadmium orange, and Indian yellow. I also used raw sienna and yellow oxide.
As I painted the central image, I also dabbed spots of each color into the background, knowing I would later blend them with parchment. That's what I did next, creating a heavier parchment in some areas for highlighting and emphasis.
Periodically, I stopped to look at the painting, and then went back to add more of one color or another. I got out the Prussian blue again and added more of that to the main image, and lightly in the background, mixing it with the parchment.
I had to be careful not to mix the colors where I wanted each one to be crisply itself. It takes practice and judgment to know when to work wet in wet, and when to let colors dry before painting over them.