Stephen Head, president of Lone Star College-North Harris, asked me not long ago what the sparrow-size, aqua-blue birds were that had shown up in his yard. He wasn't the only one who wanted to know.

Catherine McKinley is the author of Indigo: In Search of the Color that Seduced the World. You probably take the blue in your favorite jeans or denim bean bag chair for granted now, but it was once ...