Dark-colored sodas are considered worse for health than light-colored sodas because they have a chemical called 4-methylimidazole that is used for coloring, which was classified as potentially carcinogenic to humans by the International Agency for Research on Cancer. The chemical is abbreviated as 4-Mel, but it is listed on food labels as "caramel coloring" or "artificial coloring".
California's Proposition 65 law requires all sellers to disclose a warning on any food or beverage that exposes consumers to more than 29 micrograms of 4-Mel per day, and Pepsi One and Malta Goya sodas tested higher than 29 micrograms per sample in a 2013 test by Consumer Reports. Because they exceed the limit of the law, they are required to have a warning label.
The United States Food and Drug Administration does not consider the levels of caramel coloring in foods to pose a health risk to consumers. The FDA is conducting tests on various foods and beverages with the chemical to determine its safety. If consumers have questions regarding the safety of 4-Mel in foods and beverages, the FDA offers a frequently asked questions page. While light-colored sodas may not be considered healthy, they do not include 4-Mel coloring in the ingredient list.