I keep my toothbrush in one of those plastic toothbrush tubes, since it is traveling with me all over the place. I found the tube to be boring, so I tried painting right on the plastic, and later using sharpies on the plastic, but both rubbed fairly quickly. Eventually I just wrapped it in hockey tape and painted that.
I also glossed it when it was done. The split where the toothbrush tube opens is part way into the yellow stripe.
I expect the tube will actually last longer because of the reenforcement on the surface.