This is definitely not a derogatory reference to blacks. With the 3rdMarDiv on Okinawa in the 60s, it was used back and forth between blacks as well as between blacks and whites. If it were derogatory, I would have gotten my ass whupped many times. Beyond Okinawa, in VN and later in Yokosuka, the term was prevalent and used in a non-pejorative manner. The term splib was used to identify blacks or African Americans in a non-insulting way.
Where are the splib bars? The splibs hang out in the "Hole".