Thanks for the answers. A few more:
Is it possible to dim all icons and buttons (by overlaying them with a dark transparent bitmap instead of opaque) - and perhaps unblank (if possible, with fade in) when hovering?
Is it possible to blank out/dim the tray icons?
I use the classic style which isn't actually a visual style. I would need a visual style that looks like classic, one without any bitmaps, because I want one that uses system colors and doesn't impose its own.
Unless I use a visual style, to blank out the min, max, close buttons it would seem I need to hack the font.
Is it possible to remove the lines and + from Explorer's folder tree?
I'd like to be able to remove all icons and bitmaps from the UI, leaving just the button rectangles and text (if there originally was) for a command line-like visual experience, no bright spots or colors anywhere, just black and dark gray text and rectangles.