I just came across this thread, and don't know if anyone is still reading, but wanted to write, because I just put up my backsplash (in a new white shaker style kitchen). Everyone who sold the white subways said to use white for the grout. But most people in Gardenweb were saying to use gray? I didn't end up buying at home depot, but a guy there said it best. He said that the "authentic" color of grout used with subway tiles at the beginning of the century was always white. I told him mine looked creamy to me, and he said "If the tile reads white, at all, when you look at them, use "bright white". When you see subway tiles in a movie and the grout looks gray, that is done to make them look very old and that the grout has gotten dirty/discolored after many years. He said it is was in the 1980's that gray or black grout started to be used with a white tile. The brick pattern doesn't dissapear with white grout. You can still see the brick pattern under lighting because the tiles aren't totally flat. It's a cleaner look with white and authentic to the early century rather than the 80's. The original subway tile did not have beveled edges. This allowed a smooth surface as opposed to the modern tile which really defines separation in the installation.

I have the Subway Ceramics Avalon / Minas with a medium gray grout. And a Shaw's white sink, if anyone is considering that, by the way. (My contractor could have ordered it directly, but at his request, I went through a tile store, and by the time everyone had put their sugar onto it, it was OBSCENELY expensive.) I'm not an installation expert, but at least with the Subway Ceramics, the installers use little plastic spacers between the tiles (I think some others have their own spacers?) when they put them up, they don't do it freehand, so how much grout you get is a function of 1) the limits set by the curvature of the tile and 2) what size spacers they use. So you might be willing to go a little darker with a smaller grout line, or with a handmade tile that refuses to go close together, you might want to stay light. The traditional color is close to concrete. But most modern people don't seem to like that, so do what pleases you!

agree with previous posters..simple tile-blend the grout, as similar to the tile as possible..unless you deliberately want high contrast grout to accentuate it for some reason. then it becomes a decorative element on its own, and needs to be considered as such. more rustic tile that has different shape, like say star and cross mosaics, or lantern shape, etc-you want then a grout that's just a tad different in terms of shade, so it won't blend with the tile to the extent the effect of shape will be lost

my kitchen renovation will begin in a few weeks and I'm trying to decide what colour grout to put with our white subway tile. we live in a log home but decided to create an all white kitchen to contrast with the wood. The cabinet colour will be an soft white (simply white by Benjamin moore) with white countertop and white subway tile. my only issue is the grout! I don't know if they grout will be nice because of it being a log home. should I go with white grout?? thanks!!