There are two types of racketball- blue and black. Blue balls are slightly bouncier, so ideal for recreational play.
Black balls are less bouncy, and are used mainly in events such as the National Racketball Championships.
If you are new to the sport, or just fancy having a hit with a friend, start off with a blue racketball.
If, after a few games, you find it too easy, you can then progress to using a black ball.
The recommendations on which ball to use from the ESR are:
Elite players competing in national championships, regional and county premier leagues should be encouraged to play with the black ball.
Players competing in leagues below premier leagues should use the blue ball, unless both players agree/prefer to use the black.
All recreational players should use the blue ball.