going back to what you know.
trying something out, but realizing it wasn't for you, and going back to what you know. black has more of a lower connotation to it - versus going back to "white."
got into a relationship and changed aspects of the way you live and your life. got out of the relationship (exonerated yourself, more like it) and going back to your life (just the way YOU like it) = back to black.
going back to your ex, because that's what you know = back to black.
giving up staying straight, and giving in to your addiction = back to black.