M&M's Costumes allow you to dress like an M&M's "spokescandy". They vary from shirts marked with an M, to intricately designed costumes that cover your entire body. It's a fun thing to dress up for on Halloween, as M&M's are highly recognizable.
The exact date of the first official M&M costume is hard to find, most likely being between 1960-1980, because multiple colors existed during that time. Shirts marked with the letter M were the first costumes available to the general public, homemade costumes like cardboard cutouts were not popular, but creative. Later in the late 1900s, M&Ms created full-sized M&M costumes that were tights combined with a circular mask. Designs have only improved since then, while there is less variety.