The file you're looking for is taxiway_marks.bmp, and it's in the main Texture folder.
They only control the yellow markings as far as I know - and maybe not all of those. If you change to another version of that file, anything else that stays the same is not changeable. As far as I know, none of the white lines are bitmapped at all. Instead, they're auto-generated as part of the airport's AFCAD.