I really hate when lawmakers base policy on shaky evidence.
I do think that some children could benefit from dye-free diets; but not all. Make it a matter of school policy that is defined every 3 to 6 months by asking the parents to lend their voices/ballot on the matter; outline the potential “pros and cons” directly on the ballot and let the parents decide each cycle if they want school lunches to go dye-free. Additionally you could poll the children regularly to monitor for dislike of food as well as have lunch monitors just take notes on how much food is eaten.
Then sit back and watch as some schools try it out and some don’t; and you’ll have the ability to gather solid empirical data on if these are indeed problematic for children.