When all else fails......If it's more than you can stand to look at you can always cut away the grout ( no you don't have to get all the way to the subfloor but you do have to remove all the grout from the top edges of the tile ) and regrout. I would suggest you do it a shade darker than what is already there. Its a lengthy job but well worth it to not have to look at someone else's dirt.
My husband and I installed tile/ wood for about 10 years. He still does it but my body won't take the work anymore. Therefore I quilt.
