Hmm that's a good question. I don't know if grout could be stained. This puts you in a bit of a conundrum. Could you live with the tiles with the dark grout if you created the design around it? If yes, then i would suggest going with either off white cabinets or light grey as you suggested. You could make the island a charcoal grey to tie the grout colour. I think all of these changes plus the stainless steel will neutralize the charcoal grout. Your countertops need to be light and in the grey tones for sure.

If you cant stand the grout color, then dont design around a mistake. Sadly, it will cost you money to break and replace all of the tiles but to put more money into your kitchen to correct a mistake, could leave you more unhappy at the end.

I personally dont think it is a lost cause. I think the grout color is being emphasized by the brown cabinets and the black appliances. My two cents worth. Best of luck!