I hope someone chimes in with a good answer for you on this. I suspect there is not much you can do to recolor aged plastic, but in the meantime perhaps consider painting it? There are some paints that can be used on plastic, so you will have to be careful to pick one of those. You could get quite fancy (I have seen pictures of some painted machines that are almost too pretty to use), or you could go simple. You would have to be sure to not get any paint inside the machine, of course. I bet there are YouTube videos that show you how....