I've changed grout color three times in my life. Once, literally drilled out black grout. Uggh. Never again. The second time we were in Korea and the oily soot from the oil heat was in the grout in all the tile. It would not come clean even wtih muriatic acid. SO.... I cleaned it as good as I could then carefully painted all grout lines with primer and then with oil based paint. It looked perfect even when we left. Everyone marveled at how clean our house looked compared to theirs. And lastly, my kitchen was as yours. I put a page up online to show how I darkened the the grout and since I've done it, I've sealed it and it's wonderful. I didn't choose the wrong color, the charts just didn't produce what it said the product color would be. Link to the page is attached. Here is a link that might be useful: Photos and directions of how I changed my grout color

Congratulations on your beautiful new space! What kind of grout did you use? Sanded or unsanded? Epoxy? As others have said, you might want to wait to see how you feel about it. If you decide you want to make a change, and you used a regular cementicious grout you can change the color with a grout colorant. Polyblend Grout Renew performs very well for this purpose, and they have several greys to choose from, including Cape Gray below.

There are dyes you can use to color installed grout a really time consuming job even with small , straight grout lines so not sure how much you are concerned. I honestly in the pics do not see a huge difference . I think I would go to a good tile shop and see what they suggest. My gut say just leave it but thats me. Everything changes with time and I think that is what happened here.

no easy way to fix it. scraping it out might damage the tile. what's wrong w/the grout?? It looks perfectly fine. Frost is white w/a hint of gray. You couldn't have matched it better if you tried. stop fretting.