There's plenty of options available. A coworker of mine used to print out code for reviews. You can use italic, bold and underline as alternative to colors. Grayscale might work nicely for eInk too - for laser printers just thin/regular/bold probably works better.

Other fonts... I could see myself being distracted by changing fonts in a document, except maybe for comment blocks. But for those italic/thin seems to work well already.

Tried to find the tool... it's GNU enscript. Syntax highlighting for several languages, outputs to postscript.