It varies from language to language I'm sure but in C there's enough syntax and sigils and what not that it's easy to parse visually without colorized hints.
Just keep your code window small enough that it doesn't make your eyes glaze over.
I think you hit the nail on the head. I have no problems using C or Java without highlighting, but I wouldn't want to use Python or even Fortran without it, there's just not enough guidance for my taste.
Just keep your code window small enough that it doesn't make your eyes glaze over.