Flooring Tile - Grout cleaning help

I am trying to clean the grout in my house. It was never sealed. The original color was antique white and now on the more heavily trafficked areas, it is almost grey-black. I have tried some commercially available cleaners with mixed results. Is there some product that someone swears by to make my grout an offwhite color again?

Thanks for reading.

Is it sanded grout? This is a tough one, because with that amount of discoloration usually people start thinking about regrouting. There are acid solutions available you can dillute and see if that has an effect. Usually I do a 50/50 solution of white vinegar and water first and see what that does (spread it with a sponge liberally, and then follow up with a damp spong to wipe the tile down after letting it set for a couple of minutes).

Steam it, or clean it the best you can and go with a grout colorant.:)