A very large and well-controlled British study a couple of years ago confirmed that not only several common food colors (two of which are banned in the U.S.), but also the preservative sodium benzoate made hyper kids measurably more hyper. See a report here: http://www.consumerhealthreviews.com/articles/GeneralHeal...
One other thought is that he may have other sensitivities/allergies that make him physically or mentally uncomfortable and hard to please. He might be sending out signals for help but have no real idea why, if he's just always at odds with his own body.
I have severe chemical sensitivities, and get both physical and emotional symptoms to exposures to perfumed toiletries, home cleaning products, fabric softeners and air "fresheners." In group testing situations, I have watched children go from contentedly coloring to bouncing off walls, screaming, crying, or being impossibly stubborn just minutes after having drops of some dilute solution squirted under their tongues.
It would be worth checking out. You can try sealing all suspicious products in plastic bags and using baking soda or vinegar for most cleaning for the next 2-3 weeks, and watch for any improvements in your son. If reintroducing the products (many of which are toxic, anyway) back into the home then results in worse behavior, you'll have a possible solution to work on.
I know this sounds like a lot of change, but it's really not that hard to try. Most of the household products and toiletries commonly used are really not needed, and they are expensive. We believe we need them because the advertising is so compelling. But I've used very little for cleaning in my home besides baking soda, white vinegar, borax, and scent-free detergent for over 20 years. My house always smells clean and pleasant – and visitors often remark that the atmosphere is "calming." I think their bodies are noticing the lack of toxins in the air.