Santa's sleigh is mainly red with hints of gold and brass surrounding its fixtures. The colors of his sleigh match his standard suit colors of red and white.
According to Unmuseum.org, "During the 19th century, Santa was often shown wearing different colors such as purple, green and blue in addition to his traditional red." Unmuseum.org also noted that Coca-Cola was responsible for fading out the various colors and cementing Santa's image as red with its Christmas advertisements in the 1940s. Because of this, many people feel it is important to keep all of Santa's accessories the same color as his suit to avoid confusion or a sketchy history.