Beyoncé is the only black female to sell over 2 million albums in pure sales in the U.S, Rihanna is the only black female artist with a non-featured number one hit and other than the two and Nicki Minaj no other black female is selling well. During the past decades there were more than four black females being highly successful:
70s - Diana Ross, Aretha, Tina, Chaka Khan, Donna Summer
80s - Whitney, Janet, Sade Adu with the group Sade and some of the females from the past 70s decade like Donna Summer and Tina Turner
90s - Whitney, Mariah, Janet, Lauryn Hill, TLC, Mary J Blige, Toni Braxton, Brandy, Monica, TLC, Destiny's Child etc
00s - Alicia Keys, Rihanna, Beyoncé, Brandy, Ciara, Missy Elliott, Lil Kim, Mariah, Janet
10s - Rihanna, Beyoncé, Nicki
And we are already 6 years in and there shows no sign of hope