Be very careful what you use on marble; many cleaning products can permanently etch the surface. Shaklee Basic H2 all purpose cleaner will remove it safely. Do a search on the web and you'll find a distributor.

I think there was some confusion here. We are not suggesting separate color grouts. The contractor said that white grout was bleeding into the black tiles and black grout was bleeding into the white tiles, but this was done on some surplus/sample tiles just laid on tarp and tested in the garage because he didn't know what color to use for the flooring inside the house. My question is how in the world did that YouTuber get black grout adjacent to White tiles with no bleed? A certain technique or process or product we need to be looking for?

Several posts on this forum about them. As @joseph_corlett said, some people love it. They don't have to worry about their counters so much. But others, including me, think it alters the beauty of the marble. Marble is so special because of its depth and translucence, and those attributes are muted or even hidden by the protective coating. Some people liken it to Grandma's plastic slipcovers on furniture - you can still see the furniture entirely, but, oh well. Other people think it looks great, so if you go this route, make sure to ask the fabricator to see some marble counters with the protection on them first, and see if you like it. One thing that even the enthusiasts of this coating will say is that the edges of the protective coating are visible at the counter's edges. There is a school of thought that if you are concerned with etches and stains that marble naturally gets, it is a counter that is not for you. People who love marble in their kitchen are happy with the patina. There are so many other counter choices out there, most of them more durable than marble.

I would hire a professional to clean the grout and restore the tile. It probably needs sealing at this point also as marble needs to be sealed periodically - even honed marble. FWIW I have honed marble basketweave tile in my bathroom.