<P> In 1950, a black "M" was imprinted on the candies giving them a unique trademark . It was changed to white in 1954 . </P> <P> In the early 1950s, the Midwest Research Institute (now MRIGlobal) in Kansas City, Missouri, worked on behalf of M&M's to perfect a process whereby 3,300 pounds (1,500 kg) of chocolate centers could be coated every hour . </P> <P> Peanut M&M's were introduced in 1954 but first appeared only in the color tan . In 1960, M&M's added the yellow, red, and green colors . </P> <P> In 1976, the color orange was added to the mix to replace red, which was discontinued in response to the "red dye scare" over Red Dyes #2 and #4 having been evaluated to be carcinogenic in nature . Although M&M's were made with the less controversial Red Dye #40, the public was wary of any food being dyed red . Red M&M's were re-introduced in 1987 . </P>

When were peanut butter m&m's first introduced