Rosanne Cash's "Passing" Mother?

Rosanne Cash is the daughter of Johnny Cash and his first wife Vivian Liberto, whose parents were Thomas Liberto, a Sicilian American, and Irene Robinson from Texas. In some photos Vivian could almost be an exotic European type, like Sophia Loren, Victoria Beckham or Sarah Hyland, but most of the time she looks more ambiguous and mixed-race, like Rosie Perez or Eartha Kitt.

Ken Burns' recent documentary on Country Music talks about an incident in the 60s when a racist group in Alabama with links to the KKK questioned Vivian's whiteness, saying she looked like a "negro", but in an interview Rosanne claims that she was just very exotic looking because "her people were Italian", without even mentioning the Robinson side of the family.

Not everyone's buying it, like in this popular blog thread where many commenters believe she was black passing for white. There are the usual idiots repeating refuted lies about Sicilians being "African" and North Africans being "black", but one comment focusing on the Robinson line (if accurate) solves the case:

I dug around into her genealogy a bit out of curiosity – the commenters who stated that her parents (and maybe grandparents too) are white according to the census etc just didn’t dig far back enough. Also, regarding the census, it does have mistakes at time and people would just tell the census taker their info – so if they say so and so is from a certain place, or that they’re white then that’s what will be put down. Anyhow, Vivian’s mom was Irene Robinson. Irene’s mom was Dora Minnie, and Dora’s dad was Lafayette Robinson, born 1844. In the 1880 census he is listed as “mulatto” and by the 1910 census he is listed as “white,” so I’d assume that somewhere in that time he decided to start passing as white. His mother, Sarah, born about 1830 was also listed as “mulatto.” You can see various photos and family trees of the family on ancestry.com and one of them has Sarah’s mother listed as an unknown black slave and her father looks to be a slave owner by the name of William Shields. Sarah is listed in the 1870 census as “mulatto” and then in 1880 she is listed as “white.”

Anyway, here's a photo of Johnny Cash with Irene Robinson and Tom Liberto:


Which parent do you think Vivian gets her "exotic" looks from?

UPDATE: Genealogical research and genetic testing done on the show Finding Your Roots has confirmed that the Robinson line was mulatto passing for white.