Hi Joel,
The current style has evolved from input from the community. There are basic reasons for keeping it similar. Does it really have to change much?
For instance:
1. Greys (and colors near grey) work best because they are color neutral. That is, they work for people and equipment that are color blind or where a primary color does not work.
2. Italics work best in font sizes that are larger than standard, again because readibility.
3. Sans-serif fonts are generally easier to read.
4. The current doc style is fairly browser display tolerant.
I think there has been some criticism about the use of background colors for highlighting.
You could experiment by making a light grey backround around the outer document boundaries (perhaps a lighter grey background for the document background) and white to highlight the background of "screen shots" etc. This would provide visual highlights and may reduce eye strain for those who experience difficulty reading high-contrast screens. However, large grey backgrounds may be a problem if some printers print the background color. =(
Thick (grey) borders may be enough for highlighting blocks of text, so that varying the background color becomes unneccessary.