The tile is easy to keep white, the grout, not so much. That's why we use a medium gray grout... looks older and no one knows if it's clean or not. :)

I currently have white tiles on my bathroom floor with white grout. I will not choose white grout for my floors ever again- I know it looks pretty, but it is very, very difficult to clean, and is a dirty, brownish gray color most of the time. I am building a new home right now, and am using small white tiles again, but with black grout this time.

I agree with the dark grout, especially on the floor.