What is Blue 2?
Blues 2 also known as indigo dye or indigotine is a colorant used in food. The chemical compound that constitutes the indigo dye is called indigotin. The ancients extracted the natural dye from several species of plant as well as one of the two famous Phoenician sea snails, but nearly all indigo produced today is synthetic. 
Synthetic food dyes have been suspected of disrupting children's behavior since the 1970s, when Dr. Ben Feingold, a San Francisco allergist, reported that his patients improved when their diets were changed. Numerous controlled studies conducted over the next three decades in the United States, Europe, and Australia proved that some children’s behavior is worsened by artificial dyes, but the government did nothing to discourage their use and food manufacturers greatly increased their reliance on them.