Although the studies do have conflicting evidence, the FDA came out and admitted in 2011 that food dyes likely do contribute to behavioral issues. Sadly, they have ignored the CSPI's pleas to ban 7 different food dyes, despite the European Union taking action to label or remove all food dyes. In fact, companies like nutrigrain bars use dyes in the USA but use all natural coloring from vegetable and fruit sources in Europe what gives? Check it out for yourself:
ADHD:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1719942/pdf/v089p00506.pdf
http://m.adc.bmj.com/content/89/6/506.full
Cancer:
http://m.toxsci.oxfordjournals.org/content/61/1/92.full
http://cspinet.org/new/pdf/food-dyes-rainbow-of-risks.pdf
Asthma/allergies: http://orthomolecular.org/library/jom/1994/articles/1994-v09n04-p225.shtml
From CSPI:
Many studies have shown that food dyes can impair children's behavior. Research by Purdue University scientists, published in the journal Clinical Pediatrics & according to the nonprofit Center for Science in the Public Interest (CSPI), the findings are disturbing. The amounts of dyes found in even single servings of numerous foods are higher than the levels demonstrated in some clinical trials to impair some children's behavior.
❌General Mills' Trix cereal lists Yellow 6, Blue 1, & Red 40-it has 36.4 milligrams of those chemicals. Fruity Cheerios had 31 mg of food dyes. The one with the most artificial dyes was Cap’n Crunch’s Oops! All Berries, with 41 mg. Target Mini Green Cupcakes, which have Yellow 5, Blue 1, Yellow 6, and Red 40, had 55.3 mg of artificial dyes per serving, the highest level found in any food.
❌Skittles & M&M's, which are dyed with nearly all the dyes, had the highest levels found in all candies; M&M's Milk Chocolate was a close second. Both candies are made by Mars.
❌Kraft Mac & Cheese was found to have 17.6 mg of artificial dyes per serving. (It has removed dyes from some of its products).
❌The American beverages are a problem. They found high levels of dyes in energy drinks, Sports Drinks like Powerade, carbonated colored drinks, Sunny D Orange Strawberry, and 52.3 mg per serving in Kool-Aid Burst Cherry.
"Until now, how much of these neurotoxic chemicals are used in specific foods was a well-kept secret," said CSPI director Michael Jacobson. "I suspect that food manufacturers themselves don't even know. But now it is clear that many children are consuming far more dyes than the amounts shown to cause behavioral problems in some children. The cumulative impact of so much dyed foods in children's diets, from breakfast, lunch, dinner, and snacks, is a partial reason why behavioral problems have become more common."-CSPI
Synthetic dyes are banned in certified organic products. Moreover great alternatives (used in Europe) used to color foods include turmeric, annatto, saffron or paprika.