Grout

grouting

The act of grouting the tiles makes them really dirty. But after you clean the tiles with a sponge it gets better. And after the grout has cured completely you can wipe of the film of grout and the tiles shine again.
I use dark grout, although it doesn’t hide imperfections in the tiling (and it does have imperfections!), as light grout would do, but it also doesn’t get brown and dirty after a few years. And I like a bit of contrasty lines in all that white.