The color line, also known as the color barrier, in American baseball stopped players of black African descent from playing Major League Baseball and its affiliated Minor Leagues until 1947 (with a few notable exceptions in the 19th century before the line was firmly established). Racial segregation in professional baseball was sometimes called a gentlemen's agreement. This means an understanding, as there was no written policy at the highest level of organized baseball, the major leagues. There was minor league's vote in 1887 against allowing new contracts with black players within its league. It sent a powerful message that eventually led to blacks not being allowed to play at all.
African Americans created the Negro leagues starting in 1887. In these leagues, African American baseball teams played against each other.
The color line was broken for good when Jackie Robinson signed with the Brooklyn Dodgers organization for the 1946 season.