food colorings have a long and somewhat problematic history. Written evidence for their use can be found as early as 1500 b.c.e. in Egypt and Europe. Color is such a strong gastronomical cue to flavor and freshness that there are strong incentives for its use not only as an embellishment but also as an adulterant. As a result, food colorings are highly regulated, and only a handful of compounds are approved for use. Colorings derived from natural sources that have a long history of use in food are generally regarded as innocuous, although naturally derived food colorings are not necessarily safe. For example, into the twentieth century, bluestone—copper sulfate—was used in pickle recipes to give the pickles a vivid green color. Unfortunately, like many natural mineral-based colorings, copper sulfate is toxic, albeit only mildly so.
