Author and synesthete Pat Duffy describes four ways in which synesthetic characters have been used in modern fiction.
1.Synesthesia as Romantic ideal: in which the condition illustrates the Romantic ideal of transcending one's experience of the world.
2.Synesthesia as pathology: in which the trait is pathological.
3.Synesthesia as Romantic pathology: in which synesthesia is pathological but also provides an avenue to the Romantic ideal of transcending quotidian experience.
4.Synesthesia as psychological health and balance.
 Patricia Lynne Duffy is an instructor in the UN Language and Communications Programme. Duffy has given presentations on synesthesia at Yale University, Princeton University, the University of California, San Diego, Rockefeller University, the University of Virginia, and others. She is a co-founder of and consultant to the American Synesthesia Association. BLUE CATS and CHARTREUSE KITTENS How Synesthetes Color Their Worlds By Patricia Lynne Duffy
and... just in case you heard otherwise from other "indigo" sources, the designated word "Indigo" has nothing to do with the color of an aura! It is the result of scientific observations by a woman who has the brain disorder called synesthesia. http://www.indigochild.com/