It is very rare for children to have such a negative behavioral reaction to the food additive, which is generally very safe. However there are a few children who seem to be hypersensitive to it. It is also possible that younger children are more vulnerable. Certainly it does no nutritional harm to eliminate them from his diet, or any child's diet. I would caution other parents, however, who are dealing with behavioral problems, to automatically blame the child's diet without also searching for other causes, medical or otherwise.
Studies continue to try and determine if there are any causal links between food dyes and behavior.
At present data doesn't support it for the majority of children. You have determined that your son is one of the few it does, and you were lucky to find out and fix the problem so easily. For anyone else who suspects it might be a problem, a return to a diet consisting of fresh, wholesome, additive free, minimally processed foods is the way to go. Thank you for writing. You should not rely on this information as a substitute for personal medical attention, diagnosis or hands-on treatment.