I monitor several forums like this and I see a lot of questions about repairing or painting vinyl siding, and there aren't any good answers. It expands/contracts badly first of all.
If your Masonite siding is not water damaged (that is one of its failings), then you could paint it. You wouldn't want to pressure wash later unless you want to repaint snce the pressure wash would probably mess up the paint job.
I would think a good ext latex paint would be the thing to use. Don't know if you would have to prime or not; the paint instructions should tell you.