Until 1972 most tennis balls used for recreational and professional play were white. Today the most common color of tennis balls is yellow, officially called, "optic yellow." Why the change? Television. The white balls were just too difficult to follow on the small screen, especially with the rising popularity of color TV.
Of course you can now get balls in an array of colors, patterns and imprinted with whatever slogan or logo you want. But of the 325 million tennis balls produced each year around the world, most are optic yellow.
Moreover, not all tennis balls created equal. The ITF (International Tennis Association) which sets the ball specifications for professional tournament play, recommends larger, less pressurized for junior players. These come in three types: the red dot or swirl, orange dot or swirl, and the green dot. They are designed to bounce lower, move through the air slower and made to suit the height and motor skills of the player.
The red dot or swirl ball is the largest tennis ball, made of felt or foam and moves slower and bounces lower than the orange ball. It is used for very young children. The orange dot or swirl ball bounces a bit higher than the red ball, but moves slower than the green dot ball and is used to teach young children as they get more agile hitting a ball.
The green dot ball is the most common ball used for junior tennis players. Not only do they train with the green dot ball, but the green dot is used in junior tournament play. Seniors and adults with limited mobility can also benefit from using a green dot ball, because they move through the air slower and do not bounce as high as a regular tennis ball.
What to do with the approximately 325 million tennis balls that are produced each year, and about 20,000 tons of rubber waste that is not easily biodegradable? According to Wikipedia:
Historically, tennis ball recycling has not existed. However, in 2015 three companies (Advanced Polymer Technology, Ace Surfaces and reBounces) joined together to create a recycling system that incorporates recycled tennis balls into a tennis court surface. Balls from The Championships, Wimbledon are now recycled to provide field homes for the nationally threatened Eurasian harvest mouse.