A clarification: Negrita is a Spanish word for little black girl. I know it sounds close to an offensive English word, but negrita in Spanish definitely is not offensive. It is a term of endearment, like saying cute black girl. Urban Dictionary: Negrita
It’s the name of this bar, and there is another next bar, with wich it shares terrace, named Negrito (black boy). The square where both bars are located is named Plaza del Negrito, that’s the reason for the bars’ names.
And why Plaza del Negrito? The original name of this square was Plaza de Calatrava (for the Order of Calatrava Knights). But in 1850 a fountain with a statue representing a child was built there. The figure was made with dark metal, and people started to name the square as Plaza del Negrito. Soon nobody used the official name. Finally in 1940, council changed it and the square got officially the name Plaza del Negrito.