Which brings us almost full-circle to early monochromatic highlighting, where you didn't have many options besides adding bold and italic to the mix.
Your scheme reminds me of CGA colour palettes. https://en.wikipedia.org/wiki/Color_Graphics_Adapter
I think different colors/shades for different types and highlighting profiling data for functions could be useful also.
Funny you should mention profiling; I was just reading http://blog.golang.org/2011/06/profiling-go-programs.html today. The Go profiler seems extremely impressive.
a) comments. What is never run?
b) literals. What is just plain data?
c) punctuation -- mostly so it can be deemphasized.
Sample of my minimalist 'scheme': http://imgur.com/NrrS9.png