Query: In what year did the Motion Picture Association of America introduce its rating system?
Context: TCM's film content has remained mostly uncut and uncolorized (with films natively filmed or post-produced in the format being those only ones presented in color), depending upon the original content of movies, particularly movies released after the 1968 implementation of the Motion Picture Association of America's ratings system and the concurrent disestablishment of the Motion Picture Production Code. Because of this, TCM is formatted similarly to a premium channel with certain films – particularly those made from the 1960s onward – sometimes featuring nudity, sexual content, violence and/or strong profanity; the network also features rating bumpers prior to the start of a program (most programs on TCM, especially films, are rated for content using the TV Parental Guidelines, in lieu of the MPAA's rating system).