It is the responsibility of each race track to have the unique uniforms on hand to match the horses the jockeys will ride. They are called Silks.
Each uniform is registered with the Jockey Club of the New York Racing Association.
Prior to each race the jockeys are given the uniforms they will be wearing for a given race.
They used to be made of silk, but synthetic materials are now used.
The Silk Room at Del Mar has over 2,000 Silks.