The 30-year-old beauty, who has been nominated for Oscars in best supporting actress category for her role in the Steve McQueen's slavery drama, said she overcame being "teased and taunted" for her "night-shaded skin", reported Contactmusic.
"My one prayer to God, the miracle worker, was that I would wake up lighter-skinned," she said.
The Kenyan actress said she gathered strength from supermodel Alek Wek when she was a teenager.
"A celebrated model, she was dark as night, she was on all of the runways and in every magazine and everyone was talking about how beautiful she was," she said.