There are many colours of balls that you can get besides the classic optic yellow if you would like. However, there will be a different minimum order quantity for some of the coloured balls, as these ones are made specially for your campaign. Whether you want some red balls, pink, or even white, they can certainly be created for you; the quantities though may need to be as high as ten thousand.
Print Area and Positions
You can print in an area of 25mm by 45mm on the ball, and in a total of 2 positions. This allows you some more choice as to the amount of what you can get onto the ball. For instance, you might want a logo on one side and a website on the other.
A note on logos: Remember that the print area is very small, and that means that that some finer details may be lost. It's therefore very important to choose a very simple logo if you have one. Anything too fine may cause the logo to flake.
If you want to read more about what you'll need to know for customising tennis balls, you can read pur blog piece "5 Things You Need to Know About Branded Promotional Tennis Balls".