I just read this posting so I cannot vouch for the hint concerning safety for grout and tile. There are before and after pictures using Woolite Carpet Foaming cleaner: http://www.aberrysweetlife.com/2013/05/cleaning-tile-grout-with-carpet-cleaner.html I have cleaned floor tile grout that looked like various shades of black grout in an apartment my son rented...gross! The only thing that made any impact was straight laundry bleach and a scrub brush which was not healthy to breathe and, I suspect, not exactly good for the grout. However, if an owner was okay renting an apartment with white grout that was grimy black after the apartment had supposedly been cleaned, I was okay with getting it white again even if it took bleach. The place definitely looked better when he left than when he moved in.

Good morning! I had a short shift in bed. Our DD called and woke us up. She's in Senegal, Africa helping with primate research for 6 months. It's broad daylight there! In my little microcosm of tile life, I've got my next test underway. This time with a 1:2 ratio, 1white:2gray. Hoping for a slight tone down from the dark. And, I'll have to remember to start getting the soft trowel out to smush the grout into place, instead of the putty knife I used to stir it up with. That explains the multitude of scratches on my samples, if anyone has noticed. Now there's and analogy I can use in the macrocosm of my life, always use a soft trowel so I don't leave scratches. Ellendi, The grouts at the tile store are all their standard colors. They didn't offer to mix up custom grout. I'm a DIY'er and never thought to ask for them to do it. Of course I ask them to give me all sorts of advise on what I come up with! I guess they are providing me with therapy. I thought about Ivory too yesterday, but as a blending color. I think I might pick some up for blending today and see if it warms the dark up a bit. Having an ever so slight peach, to the Ivory grout, it might mix with the dark gray and move it to a warmer tone. I'll reevaluate, it may be something I'd like straight and on the rocks, :) couldn't help it. BTW, my grout is sanded. This morning the dark gray looks a teeeny bit lighter, and the center has receded a bit so may not look as flush as it did yesterday. Yesterday was a rush job, using a hairdryer to dry the grouts. It must have dried even some more overnight. Don't strangle me if after all this I go with the dark gray. Getting the hairdryer out and another cup of coffee before I get ready for work...

Re grout: I would think a darker option would end up looking much like the bottom portion of the picture you posted ... in other words, awesome! I think it would emphasize the pattern, which would be my preference, too. As far as sealer, I've had good and bad experiences with natural stone. Best thing I can tell you is to take a little scrap piece and slap some sealer on it. If you like the various subtle color variations here, though, I'll bet you'd be happy w/any changes sealer might effect. And I think sealer is always a good idea for natural stone in the kitchen.

The TCNA standards; for all grout joints 1/8" and over use sanded grout. For all grout joints 1/8" and under, use non sanded. You can see at 1/8" you have a choice. Where possible we always use sanded grout as it is stronger than non sanded. Have you looked into Fusion Pro (Custom Blend), Plasma (Laticrete), or Flexcolor CQ (Mapei) as a grout? They are virtually stain proof and require no sealing. SUre they will get dirty, but the color will always be perfect.