It's brown. Nobody can guess from a photo.

If you visit a tile store, it's likely they will have a kit like Pros use which has actual samples of the grout that can be placed between your tiles so you can see the finished product. Just remember the more irregular the tile, the wide the joints have to be to accommodate the irregularities of the tile. Grout always darkens with age, so don't go too dark to begin with.

The color in the first picture you posted looks like standard gray grout.

Third or fifth in from bottom of pic. See what we mean? You need to go To A TILE STORE: ) Taking a left over tile with you? Even better.

OK, OK - I give! I've seen grout samples before. I just thought someone might have a guess as to the specific color. How about I post again later with my grout samples?

Don't know where you live, but here in the southwest, grout for Saltillo tile is traditionally grey. That being said, you are, of course, not limited to that. Get samples, choose what appeals to you.

Have they written a song about grout selection yet? I really think we are due : )

It the terracotta sealed already? It may make a difference in grout colors. Mapei makes a great color. Sahara Beige that is very chameleon like. It looks both gray and more brown depending what it's around.

I am wondering if what is in the inspiration photo is a mortar mix, I know it is used quite a bit with terracotta tiles. Have you looked at mortar mix and what that might look like next to the tile? I am fan of standard gray with terracotta, and usually mortar provides that without driving yourself bonkers with grout selection options. Could be worth a shot. Good luck :)