Thanks all..... I was fretting over hand painting the white walls so here's what I did. I found a jar lid that is the size of the inside hub (part of the wheel to remain black). On a glass tabletop I taped 3 rows of wide masking tape that would be wide enough for the lid, traced around the lid with an exacto knife to get a perfect circle to cover the inside hub of the wheel. The most difficult part was positioning the circle of masking tape on the wheel. It's not perfect, but at least the lines are clean at the white/black transition.