They never, actually, show Revan's face. He's always looking away, behind a mask, or concealed by the hood of his cloak.
This is true. However, being that it is Bioware who created that face with long brown hair, in that exact same style, for their game, I think it's pretty safe to assume that it's what the artist had in mind while doing it-- to make it canon or not. You can clearly see long brown hair in the style of the template used in Kotor, even without the face. Here
is a nice shot of his head from behind.
I think fans misinterpret what being "canon" does to something-- it simply makes it what the galaxy far, far away sees it as; if you don't want to do it that way, by all means, don't. However, if it's ever referenced again, which is what fans obviously want, they need a solid stance to take; gender, side, looks, etc.
It's for editorial necessity, not to detract from your experience at all. Developers, writers, and the like want fans to have that immersion when they play the game. They just also must take into consideration that characters may be explored further. Case in point: Jaden Korr.