I have learnt that the grout always dries lighter than those little plastic color samples, so I try to pick a sample that is just a bit darker than what I think would be the prefect color.

Just did some grout in the master bath and I used this method. While I was deciding on the grout, I had a designer friend (who had samples of my tile) look through and come up with her own suggestions. Our choices were pretty close, except that I chose one shade darker for all the grouts picked. I went with my darker grout selections and it was the right choice.

I had the same problem. I went to great pains to choose the right color tile with a matching slate colored grout. I finally found the two together on a wall sample in the tile store. Instead the grout came out light blue! My kitchen guy had the Bostik grout rep. come out. Finally we purchased Bostik Grout Stain in Shadow and the tile guy painstakingly with a little brush went over it with the darker stain. It worked for us even though it wasn't exact. I agree with chispa. Choose the grout in a darker shade. I've heard this is a regular problem that the grout samples don't match!

I've recently been told by a tile guy that grout always dries one to two shades lighter than the sample. Thankful the shower will just be white.

Well, I know what you mean about picking a darker grout, but charcoal was the darkest option, as far as I recall. I would live with it before I'd have him take it out,or I would stain it myself, if I had to, prior to sealing. It is a small room, but latest conversation with GC indicates that tile guy has agreed to come back out and do some "acid cleanup" before sealing. Which could just mean dilute vinegar for all I know... will let you know what happens.

I am just trying to get the floor to read as more or less a solid color since it is adjacent to a concrete floor almost the same color. Heck if I'd wanted a light gray, I would not have picked Charcoal! But maybe the sealing will help darken it as well. I know when I put a little water on it, it is the right color.

Test your sealer first in a hidden spot or just do a dot before applying it to the whole surface. Some are called "enhancing" sealers and they will make your grout look like it does when it is wet.

-Babka

Well, I couldn't get him to come back, but my GC said that what the tile guy was referring to was a dilute sulfamic acid solution. I looked into that and did it myself. The first time, it was too dilute, so I ended up going over it three times, with a thorough rinse in between. The color evened out, but it is still lighter than I'd like. It doesn't look bad as it is, but when it gets water drops on it, it looks just right.

Now I'm trying to figure out if I should seal it (with 511 or something else? that's what I used on the walls and it didn't change the color) or if I should go whole hog and use a grout colorant? I understand that if I seal it and don't like that look, I'd have to remove the sealer in order to apply the colorant.

I've looked into Aqua Mix, I looked at the bottle of Polyblend Grout Renew at Home Depot. I understand Mapei has their own product as well. How on earth do I decide? All I want is a dark gray. It's a very small room, so whatever I do, even if very tedious, won't take that long. We are not living in the house yet, and have another bathroom, but I'd really like to be done with this!

Thanks for any insights.

Take another look at Babka's post two posts up. Look at an enhancer. Essentially, enhancers give you the same look that you get when the grout is wet. You'll find that enhancers are also sealers. Enhancer/Sealer.

Thanks Mongo (and babka). I'm still having trouble with the terminology and with picking a specific product. Most with "enhancing" in the name indicate they are for sealing stone, but I guess that doesn't matter? They also seem to come in fairly large quantities. (I honestly have maybe 25 linear feet to cover, at 1/8" I hate the idea of buying a gallon and having to figure out what to do with the rest... )

Any specific product recommendations? Just use the stuff people use on their slate and travertine? I would live to get this done next weekend, so something from a big box store would be easiest, but I've waited this long, so I want to get it right!

Enhancers are typically advertised for natural stone. They brighten it up, giving the "wet look" but without the bright sheen.

Miracle 511 is sold at the HD (I think?) but yeah, the smallest is maybe a pint. Probably $30.

Use what you need, then try to resell the unused 15.7 ounces on Craigslist. I kid you not, someone will probably buy it.