Turns out many cables are sheathed with PVC, and will take the same oil-based stains as PVC pipe. If you want a purple cord, for instance, you can treat a white PVC cord with purple primer. If you want some other color, it is easy to prepare your own custom stains from clear PVC cleaner and concentrated solvent dyes.
I’d love to see a totally minimalist all-white office with a brightly colored cable for a pop of color. (Did I mention that this office is also very clean? A girl can dream, can’t she?)