A mouthpiece for a brass wind musical instrument is composed solely of a colored polymer material. Its size and shape may be determined by computer coordinate measurements from a conventional metal mouthpiece. The color is chosen to suit the particular purpose of the musician playing the instrument, such as to match the uniforms of a marching band. The mouthpiece is fabricated by injection molding to substantially the desired size and shape. A secondary machining process removes imperfections such as flashings and gate blushes. Alternately, a blank may be injected molded, and the blank machined in a primary machining operation to the desired size, shape, and surface texture. The mouthpiece may also be manufactured by machining a bar of polymer material. The mouthpiece functions in the identical manner as prior metal mouthpieces, but it is much more comfortable to play in cold and hot environments, and it is less costly and more rugged than metal mouthpieces.