edit: Sorry, it was the red ones that were "banned" for a short time. The public was frightened of red dye, even though according to Mars, they did not use the red dye that was suspect.
https://en.wikipedia.org/wiki/M&M's#Color_changes_summarized...
The US is terrible for substance safety. Dire. Awful. Hell, on the note of colouring, you still use bloody anthracine red, which has been banned for decades in the rest of the planet, as its carcinogenic.
So, I was a little unclear: I offered two arguments against the CRS/MSG connection: first, that MSG is a scary-sounding name for a chemical that plays a central role in our metabolism and nervous system; second, that studies have attempted to isolate MSG as a cause of CRS and failed to find a link.