SACRAMENTO, Calif. — This Easter, Americans will devour more than 1 billion Peeps — those radiant marshmallow chicks whose appearance on store shelves each year is as much a herald of spring as azaleas at the Masters. What makes the treats so vibrant is erythrosine, a chemical that shows up on ingredient labels as Red No. 3. It's one of several chemicals, along with titanium dioxide, used to color some of the most popular candy in the country — including Skittles and Hot Tamales. Both chemicals have been linked to cancer. More than 30 years ago, U.S. regulators banned Red...