My parents experimented extensively with my childhood diet's impact on my ADHD, and found that Red 40 made me bounce off the walls. The effect was dramatic, even compared with eating sugary non-Red-40 foods.
I recall a friend was relieved when Red M&Ms went away, because she had an anaphylactic reaction to them. Though I guess the real reason was the old color turned out to be a carcinogenic. It was years before they added them back, with Red 40 instead.