If you cut the masking tape into very thin strips it will bend around the spinner much better than a wide strip. I usually use 1/8" (or even narrower) strips for things like that, and it helps a lot. Make some pencil marks around the spinner the same distance up from the bottom so you'll have some guide points for your tape. Once you have a thin, straight band of tape around it, you can add wider strips that just stick to that band since they won't have to be so straight.
Yellow is a terrible color to paint, I hate it. I'd almost be tempted to paint the whole spinner light gray, shoot the yellow, then mask it for the red.