I think that is a personal preference. My personal preference is I like my grouts closer in color to the tile. But many people prefer that the grout stands out, I like it to blend more so I would chose darker.

According to the tile contractor it should be white. We want the glass to stand out not the grout so maybe going the darker route would be better. We've already had a disaster with how it was installed and want to avoid another disaster.

Thanks!

If you want the tile to "Pop Out," use the white. I would use a grey to closer match the tile. Dealer's choice here...

Is the spacing between the tiles uniform? If it is, the white grout will be fine, if it is not, you may want grout that more closely matches the tile so the spacing is not as obvious.

I wouldn't use white anywhere in that installation, but that's just my personal preference.

Mock up some tile/grout samples using several of your ideas. Thats what I did and was so happy that I did not use white on my marble after seeing it in the sample.

I always like to match the grout color to the tile color.
Also the grout width is too wide in my opinion. Less grout, is better.

Thanks everyone for responding. We decided to go with a darker grout and smaller caps. Can't wait to see the finished product :)