Wouldn't dirtier than black be more fitting?
These words should work too (via your friendly neighborhood thesaurus).
begrimed, black, blackened, cruddy, crummy, disheveled, fecal, feculent, foul, grimy, gross, grubby, grungy, impure, loathsome, miry, mucky, muddy, nasty, obscene, offensive, putrid, repulsive, revolting, scummy, sleazy, slimy, slipshod, sloppy, slovenly, smoky, soiled, soily, sooty, squalid, unclean, uncleanly, unkempt, unwashed, verminous, vile, yecchy.
The postman will always be late when you are waiting for stuff 
It doesn't help i keep looking out the window too
