Wait till the counters are in then get sample tiles to make sure you like it. After you get the tile for your project, make up a sample board of the tile you choose using double stick tape. Pick one or more grout colors that you might like, then mix up a small batch and grout the sample board(s). LET IT DRY (overnight, as it will lighten up). Then see if you like the color for your kitchen. We ended up picking the 5th color we tried. Good luck!

From what I understand from our contractor the tile dictates the grout size. I should add that because your tiles are larger and they are going on the floor, you may want to consider a 1/8" grout line. If we were talking about a uniform subway tile back splash - 1/16" grout line works (and I think are more preferable on vertical surfaces). 1/16" seems lean for that tile size. If your tile has variation even by a minute amount you will want a larger grout line. I am sure others will say 1/16" is doable, but it makes me nervous because you are depending so much on the skill level of your installer. I have 12 x 24 in my home and I did 3/16" and am very happy with them and feel like it looks very appropriate with the size of the tile.

You can use a light colored grout with your Tantrum tile. If you want you can check out glass grout, it is more translucent and never needs to be sealed. It is more expensive though.

Efflorescence will grow out of the grout and will leave a chalky residue on your fingers if you wipe it. If the installer did not use distilled water when mixing the grout, what you're seeing are the minerals in the water that have gone to the surface of the grout when it was curing. Very common especially if you have hard water. Use a flat head screw driver or a knife to etch the surface of the grout, scraping away at the top layer. You will see the true color of the grout below this top layer. Also please note, if the installer used too much water when cleaning the tile after grouting, this too call pull the color pigment from the grout causing it to look very dull.