Does anyone know anything about the newer more durable grouts reacting with stone sealers? I just had Luxor gold stone tiles patched into my bathroom wall and it looks terrible. The new tile matched the old perfectly before grouting, but after grouting the surface took on a gray hue, caused the tile surface to appear mottled, and all porosities took in the grout. My installer showed me the color of grout he used and it matched perfectly, but appeared a shade or two darker on the completed wall. He said it had something to do with the newer improved grout reacting with the sealer he used. He used nanoscrub to try to make it look better and that helped but it is still unsatisfactory.
"Newer more durable grouts" is kind of vague. I assuming that the grout was a two-part epoxy, urethane based, acrylic plus silicone, or some other non-cement based grout from you have said.
In my experience these don't react with sealers and most don't need sealing. They are however not so easy to apply correctly. Cement based grouts leave a haze that can taken of with cheese cloth or more commonly now a scotch-brite type pad. The non-cement products have to be cleaned very well from the face of the tile before they cure. Some products, like Custom's Fusion Pro (with is a pre-mixed acrylic and silicon resin combination) will dry quickly and cleaning water (if it is water cleanup, epoxies I've used are not) has to be changed regularly. The haze will stay stuck in porous materials and even with a stripper can be tough to get rid of. Depending on what the stone surface is, and Luxor Gold is a honed finish natural limestone if I recall correctly, it can be "rehoned" with a polisher and appropriate grit to match the existing hone, this is essentially mechan. It makes a mess to do it. If the surface isn't too porous then a stripper can be used (if the grout has a chemical stripper that will work, most epoxies do not) to clean the grout residue from the tile. But since it has a sealer on it, the sealer has to be removed also and natural stone needs to be sealed, after the grout has fully cured, even when many of these modern grouts don't need to be sealed themselves.
To troubleshoot what went wrong, you may take some left over tile and grout and the sealer and do some experiments to see if the problem can be replicated and what the recipe is to replicate it. Then try methods to fix it on the test tiles to see what works best.
TL;DR It is my guess a product like Custom's Fusion Pro was used and was not cleaned well from the surface of the tile before it dried. The fine haze of products like these tend to off from the grout color and usually look pretty bad a day or two after grouted. These hazes have to be either mechanically abraded off or removed with chemical strippers. Some epoxy products do not have chemical strippers and have to be mechanically stripped. Test any attempt to mitigate the problem in an inconspicuous place if possible or preferably some left over test tiles.