I am not the author, but I imagine that it could have started out as just a preference, but turned into great hatred as they kept on being introduced in more and more places. I don't mind colour, but really dislike incorrect colouring (not enough to any effort to do anything about it). Or maybe she really likes colour, but likes to use it very sparingly so it highlights things more effectively. I think there can be plenty of reasons, and I would be unsurprised if her reasons are ones that I guessed