Hi there, I came back to update this topic. No, there is no way it was mildew. The apartment was extremely dry, actually, during the winter months, and the discoloration went all the way through the grout. The Starquartz company has been a nightmare to deal with. They sent a nice representative out about a week after I posted, who immediately promised to send me new grout and $500 credit for my contractor. Well, guess what? I emailed and called for 5 months (!) and nothing ever happened. It was an empty promise. Finally, I found out from my contractor that another person had the same problem, so we spoke, and found out that others also had this issue. It was DEFINITELY a quality control issue on the part of Starquartz company, as there were several of us affected by the "bad batch" as a rep referred to it. The long and short of it is that the tile store that my contractor bought the Starglass grout from (Artistic Tile in NYC - good place!) issued me the $500 rebate and charged it back to the company, and then they forced Starquartz to send us the promised 3 buckets of diamond white starglass grout. The only problem was, after 4.5 months of waiting and calling, we HAD to get that bathroom done so by the time they sent the 3 replacement buckets in late June/early July, totally out of the blue as Starquartz had not contacted us about it, ever, we had regrouted about 3 weeks earlier with regular cement grout. (The contractor had dug out the bad grout many months before in anticipation of receiving the promised replacement, so the bathroom couldn't be used for all those months.) Caveat Emptor!

A similar thing happened to us with some kitchen floor tile. It was pre-cast/pre-finished terrazzo, and the company had very specific instructions about installation and a very helpful rep to answer questions. I gave all the info to the contractor. He ignored it and then wanted me to pay him to do a normal polish finish like they would do on unfinished tile. I refused and live with imperfect tile because the alternative was ripping out the kitchen and starting over, and a legal battle to get him to fix it. At least I refused to give him extra profit. About changes... Yeah, they treat every change like you're an indecisive idiot and act like they've never heard of such a thing and they use it as an excuse to charge big for it because you have no alternative. They use change orders as their personal ATM machine. I'm not sure how to avoid that, except to have an agreement about competitively priced change charges before you start.

I'd be concerned about the grout colors matching up. Even within the sam ebrand, there can be small variations. If you choose the glass tile, choose epoxy grout for the whole install. If you are into simple lines and easy maintainence, using the same granite would seem to fit your style better, but not just for behind the range. For the whole backsplash on the range run. Doing a combo of a large format tile, small accent tile and granite slab is too busy. A single slab of granite is serene and unifying. It's a cleaner look. And easier to clean. And while I can see using the glass tiles on the other run of counters, I can't see using that large format tile at all. It's too white with the granite, and needs to have some kinship with the other elements in the room to look like it belongs. With the elements you've pictured so far, it looks like an orphan.

Once you touch it you own it. 4x16 is a large tile for a backsplash. If you have a cooktop be aware simply boiling a pot of water on the back burner can crack the glass due to thermal shock but I'm sure whomever sold you the glass warned you:)