Here's where it's at a day later. Because I used flake white for the background yesterday, it is touch dry and can be painted upon without any tackiness (oil painting with flake white is a noticeably different experience than using any other white).
I'm now working up the foreground, developing the boot on the left. For the most part, I'm attempting to finish each section completely and move on to the next, rather than follow the more common oil painting strategy of painting in big shapes throughout and then refining in later stages (not that I won't go back and fix something if needed). I can see now that a few of the lines and curves need to be slightly adjusted for perspective.
As I noted earlier, I'm not using black. The base color consists of a mixture of pyrol ruby and viridian, lightened with flake white and toned with varying amounts of ultramarine blue, burnt umber, and burnt sienna.