Apply an even coat of spray paint to the ball. You can use primer or white paint for this. Several coats of spray paint will most likely be necessary. Sand with fine-grit sandpaper in between coats to get rid of any irregularities, bumps, etc.
After the iris has dried, paint squiggly red lines on the side of the eye, headed up toward the pupil and iris area. The more random and uneven the lines are, the more natural it will look, so don’t be afraid to experiment a little.