Re: Red dye #40 anyone?
A couple theories ...
The gut lining & the blood-brain barrier (BBB) arise from the same embryological tissue. Studies suggest that in some cases where the gut is compromised/leaky, the BBB is as well. So stuff that normally would not get into the blood stream is not only passing through the gut wall, but getting into brain blood circulation as well. So it is possible that if a "dual leaky" is occurring, then the dye is irritating the brain directly.
Another possibility is that the dye is messing with neurotransmitters and/or immune function in the gut, which may also affect brain function & behavior.
Modern medicine is only beginning to understand the gut, which beyond it's digestive functions, plays a huge role in immune function (the GALT system), and is a major manufacturer of neurotransmitters, equal to or surpassing, and interacting with, brain NT manufacture.
Don't worry about people who look at you like you are crazy. IME, a Mom who is confident about what works/what hurts for her child is respected. Some people will want to know more, but in most cases just a straightforward approach is best. If a doc questions, allude to observations, statistics (on behavior, if you have them) and elimination & challenge facts. That's generally well-accepted.