If you expand the definition of a "startup" to include tech-enabled companies, you will see a large number of companies backed by Black women, many of whom are making millions.
Some quick examples are Marve Frazier at Moguldom Media (Bossip, Madame Noire), Natasha behind YBF, and even myself. Some of us have investment, including traditional VC firm/PE, like Heather Hiles of Pathbrite, Zuhairah Scott of Kahnoodle, and some of chose not to go that route.