"if you was white, should be all right,
If you was brown, stick around,
But as you's black, hmm brother, get back, get back, get back"
So he makes "back" refer to the back of the bus and segregation.
"Brown", who could still stick around in the song, now refers not to light-skinned Blacks but to Latins, who can stick around in the country.
"Yellow," for Asians, is thrown in by Lowery. I don't know how they should take that "mellow" bit. Does "mellow" mean not stressed out by other people or not being so uptight oneself?
I'd say on the whole it was a little embarrassing. The same point could have been made in more general terms without singling out each race.
It means that Asians should accept being discriminated against, and counted as worse than white at Affirmative Action quota time.