The light skinned actress put on dark make up to play Simone. This is especially wrong because Simone's dark skin is a part of her life and legacy. I'm a pale man and totally unqualified to explain colorism so here is a link.
Light-skinned for a black woman. Historically, lighter women were sometimes able to 'pass' as white, so it's a term with a lot of significance. Even today there's a fair amount of colorist (in both directions) in some communities.
http://www.vox.com/2016/3/4/11161980/nina-simone-saldana