Uniforms in baseball have undergone many changes since the 1960s. Through the first half of the 20th century, baseball umpires went to work as if they were going to a formal business meeting. The outfit included a black sports jacket, a white shirt, a dark tie and dark pants. The jacket and pants were made of wool, and the clothing requirements never changed despite the temperature.
Umpires are commonly referred to as "blue" during conversations with players, coaches and managers. A player may say "timeout, please, blue" when making that request. However, umpires no longer are required to wear blue jackets. In the 1960s and 1970s, umpires wore black or blue jackets and matching pants. However, umpires often wear maroon jackets to go with gray pants. Minor league umpires wear varied color combinations.
During the 1970s, National League umpires began wearing long sleeve blue shirts and eschewed the sports jacket. By the 1980s, they started wearing short-sleeve cotton shirts for greater comfort on hot summer days. American League umpires got rid of their sports jackets a few years later and also allowed their umpires to wear short sleeve umpire shirts.
Windbreaker Style Jackets
Umpires began wearing windbreaker-style jackets in the 1980s when adjudicating games in cold weather. These jackets offered greater warmth and flexibility than the sports jackets they'd worn previously. These jackets are pullover style and include a pouch in the front for placing hand warmers. "Having hand warmers can be quite essential when you are doing cold weather games," said former NCAA umpire Art Singer. "You don't have protection for your hands, so warmers are essential."
Uniform Numbers On Shirts
The umpires are all assigned numbers by the major leagues. Until the 2004 season, the umpire numbers were not placed anywhere on their uniforms. However, in that season, umpires started wearing their numbers on the sleeve of each shirt. Those numbers are visible in warm and hot weather but not in cold weather when umpires wear jackets.