Diet recomendations

So I have never really followed a diet regimen designed by someone else. I just feed my family in as healthy a way as possible/convenient (whole grains, organic when possible - I limit sugars, but we don't go without) and we are a pretty healthy crew.
I noticed a mama in the medical needs forum had an episode with her dc right after some red dye. It helped me make the connection with similar behavior in my dd after a red popsicle at girlscouts, since she doesn't get this type of thing at home.
Dh is ready to help me commit to a more regimented diet for our family to see if it would help youngest dd's behavior. Any suggestions?
Thanks

Some of the changes we've made as a family (we are vegetarian, so that wasn't a change we had to make) have been:

eliminating transfatty acids and replacing them with healthy fats. Fats affect our hormones and brain function as well as heart health. Transfats displace the good fats and can lead to many illnesses as well as exacerbating some mental issues. Look for partially hydrogenated and look for fat numbers that don't add up (ie saturated fat 3 g, unsaturated fat 3 g, total fat 11 g). Soon it will be required by law to list transfats, but as of yet not all food products do.

replacing artificial food coloring and flavoring with natural. This is actually fun, and only a bit more work. Saffron, turmeric, beet juice, cherry juice, blueberry juice, red cabbage juice, aronia berry juice, etc are good for coloring. There are several internet resources for what to use for what color. For natural flavoring one can either make their own (for instance maple syrup or extracted fenugreek make good maple flavoring) or look for organic natural flavors.

using whole grains and whole grain products whenever possible.

eating organic dairy/eggs and eating more (and organic when possible) fresh fruits and vegetables. Especially important are the dark leafy greens (such as kale, collards and chard). Those are rich in Omega-3 fatty acids which are very beneficial to so many parts of the body.

using healthy sweetener options. We too don't go completely without, what we've done though is switch to organic unbleached cane sugar (or turbinado, whichever is available), organic molasses, grade b maple syrup and raw honey. One can also use succinat or brown rice sweetener (if they're available where you live) or agave (cactus sweetener).

eliminating preservatives (except vitamin C). sodium benzoate and its relatives are awful for exacerbating behavior in children. There's even been a few studies in Europe to this effect and they're being phased out there.

Thank You Christine!
Just what I needed to bump our diets one more notch in the right direction!