>Well, no. One of the basic rules of thumb in typography is that, when writing a piece of text, you should choose one typeface and stick to it. Likewise, a splash of colour may grab the reader's attention, but it will inevitably decrease the legibility of the text. The natural flow of the text is broken, and it takes more brain effort to piece together the individual letters into words and semantics. Cognitively, the reading process becomes slightly less automatic and slightly more conscious; leaving less room in the conscious part of the mind for actually understanding the text.

That might be true for text, but I don't read code at all the way I read prose. I highly doubt i've ever read more then four or five lines of code in a row without my eye jumping to other parts of the function, forward to the next part to understand why variables are being set up, or backwards to remember when such variable was defined, or jumping to the big picture to remember how this function or that fits into the overall program. Syntax highlighting is enormously helpful to my eye when reading in that manner.