Also related to this topic is a book by Catherine Slaney, "Family Secrets: Crossing the Colour Line."

Catherine is a descendant of Anderson Abbott. Her family branch chose to "pass" and she only learned about her heritage later in life. The book has a good deal of history, photos and Abbott genealogical information.

http://www.amazon.ca/Family-Secrets-Crossing-Colour-Line/dp/1896219829/ref=sr_11_1/701-7013741-8525166?ie=UTF8

It's a very interesting book.