When running in a race, horses are allocated to a "bracket," a grouping of one to three horses in a race (for example, horses in barrier No. 1 and 2 are "bracket No. 1," and barrier No. 14, 15 and 16 are "bracket No. 8"). This "bracket" system is a unique aspect of Japanese racing.
Each bracket is designated with a color (for example, bracket No. 1 is "white," No. 2 is "black," so forth), and the jockey's cap color is decided by the bracket number of the horse. This makes it easier for fans to locate their picks during the race, whether he/she is watching it on TV or from the grandstand.
If there are nine runners in a race, bracket No. 8 will consist of two horses, while the remaining will have one horse each. If a race has 15 runners, all but bracket No.1 will have two horses each.
In addition, each owner has his/her racing color and jockeys are required to wear them in the race. Therefore, if two (or more) horses of the same owner are allocated in the same bracket in a race, JRA requires the jockey to wear a two-colored cap, in order for the viewers to identify and distinguish the horse with the same racing color.