One thing I've been doing for a few years now is minimizing syntax highlighting for code, and using some of the colors I save to have different kinds of comments with different colors: http://i.imgur.com/vU783Xo.png

Here's the initial idea that led to this: http://akkartik.name/post/2012-11-24-18-10-36-soc. As you can see, it was in turn spawned by.. a comment on HN :)