They stopped making red M&Ms for TEN YEARS.
In the 1970s, scientists in the Soviet Union claimed that Red Dye No. 2 dye caused cancer. At the time, the dye was so commonplace that it could be found in everything from ice cream to makeup to sausage casings. It was also never officially linked to any deaths or illnesses.
Regardless, the widespread panic over the cancer rumors netted Red Dye No. 2 a ten year ban from the U.S. Food and Drug Administration.
This led to the Mars candy company removing red M&Ms from their lineup. This was despite the fact that red M&Ms didn't even use Red Dye No. 2!
(source)
