black up

verb3

1. •
   To become or make (something) black or darker.
2. •
   To put on or wear blackface makeup.

   • Cantor starts blacking up, right then and there, painting his face with a burnt piece of cork. — 2016
3. •
   To make something (e.g. a film, cast, story line, etc.) more racially black in character; blackenize.