Well...do you see things as either Black or White? Good or Bad? Opinionated? Do you judge yourself and others?
If yes...it's simply a matter of stepping away from yourself a bit to get a higher perspective and realizing that we're all unique and there is no good or bad. Dark or Light.
The blackness that you threw up would represent some darkness or 'bad' thing that you might feel is lurking within you.....and the white cloth may represent the purity and goodness within you.
See? That's pretty black and white. No gray. Nothing in between. Successful or a Failure. It may be that you judge yourself too harshly because you see things as either good or bad - but nothing in between.
Does that make any sense?
Remember - the dream could be about your relationship to food, too.