I'm reviewing the literature on the link between food dyes and hyperactivity.  Studies evaluate hyperactivity largely by observations made by teachers, psychologists, and/or parents.  Observations by trained professionals using defined scales are sometimes considered superior to observations by parents.  However, a meta-analysis of 15 studies (Schab+Trinh 2004, "Do artificial food colors promote hyperactivity in children with hyperactive syndromes?", Developmental and Behavioral Pediatrics 25(6): 423-434), found that:

While health professionals' ratings (ES = 0.107) and teachers' ratings (ES = 0.0810) are not statistically significant, parents' ratings are (ES = 0.441).