



The only requirement for surface is, to have irregular marks different to the background - so, any contrast combination of colors is possible, and even invisible to the eye infrared one (with visually smooth uniform surface) was mentioned in Logitech patent. In practice, though, only single combination was ever manufactured: red balls with black speckles on them.
Logitech Marble Optical Technology White Paper:
https://trackballs.eu/media/Logitech/marble_wp.pdf
Detailed description of technology in patents US5288993 and US5703356:
https://trackballs.eu/media/Logitech/US5288993.pdf
https://trackballs.eu/media/Logitech/US5703356.pdf
Technology was used in all Logitech optical trackballs prior to laser models.