Micks juvenile outpouring of interracial enthusiasm. Or so he says, nowadays. The lyrics of this song are so scandalous in our ears, that it was taken off the setlist of the 2021 US tour. In between, a mass of articles have been written about this song, mostly about those misogamist lyrics.
Brown sugar can be read as referring to a black woman, or to heroin. In Mick Jaggers case it probably was both. It was also about slavery, about women that were bought in slavery to be raped. By extension, also about slavery to the brown sugar heroin.
Curiously, my version has a nameless cover from Radio Veronica. It makes me suppose this was used for the radio station. Since the single is from 1971, that would make this the original radio station, on a ship before the coast of the Netherlands. They existed that way between 1960 and 1974.