Colour can help carry information. It is a lot easier to identify strings if you use colours rather than just rely on seeing opening and beginning quotes. I know that I find it very useful - and even more so my choice of colours for comments making them blend more in the background and making it easier to forget.
I would liken it to the use of boldface letters to represent matrices (or vectors) in some math textbook: without this convention, you have to rely a lot more on memory to know what each symbol represents. Mathematicians and physicists everywhere have found this to be useful.
When you have a huge majority of programmers using syntax highlighting, you have to ask yourself if there is not an instrinsic value to its use and, if so, perhaps try to use it to communicate with the larger community, rather than adopting a cliquish practice.