For decades, researchers have been trying to answer a hotly contested question: Do the synthetic dyes used to add vibrant colors to foods like certain breakfast cereals, candies, snacks and baked goods cause behavioral issues in children?

A bill before the California Senate, which is expected to come to a vote this week, has reignited the debate. If passed, it would prohibit K-12 public schools in California from offering foods containing six dyes — Blue No. 1, Blue No. 2, Green No. 3, Yellow No. 5, Yellow No. 6 and Red No. 40.

Between 1963 and 1987, the Food and Drug Administration approved nine synthetic dyes to be used in foods in the United States, and the agency maintains that they are safe.

Yet some studies have raised concerns that they may have an effect on some children’s behavior.

What the Research Suggests

In the 1970s, a pediatric allergist from California caught the attention of physicians and parents when he suggested that a diet without artificial food colors, flavors and preservatives could help treat the majority of children with A.D.H.D.

That was an enthusiastic but exaggerated claim, said Dr. L. Eugene Arnold, a professor emeritus of psychiatry and behavioral health at the Ohio State University College of Medicine. Ensuing research from the 1980s “pretty much debunked” the idea that strict elimination diets were helpful for treating A.D.H.D., he said, so many physicians concluded that they were ineffective.

But scientists continued conducting trials on one element of the elimination diets — synthetic food dyes — during the next decades.