Try a poultice to suck the contamnation out of that crack. When you get it decontaminated, tint some super glue to match please.

take a small sharp tool (like a dental hygenist metal pick) and try to carefully scrape out the gray grout. when you have a slight divot, fill it w/same color unsanded white grout to match the marble, or, try mixing some ground up tile (marble is soft. take a spare tile piece and smash it to a rough powder texture, mix it with a bit of white grout, and fill the divot w/that) or mix the powder w/the super glue.

try practicing on a spare tile first.

honestly tho, I don't think it's a big deal. a few other tiles have some gray line in them.

These are amazing ideas!!!! thank you Beth and Joseph.

Btw, joseph, what is a poultice?

a product used to draw out something. on marble, it's used to draw out a stain or colorant.(but I don't think this is going to work on the grout)

on the body it's used to draw out infection or treat a variety of ails like inflammation, pain, etc

another thing to try, 'grout colorant'. try and match the marble with a grout colorant like Grout Renew, and light paint the color onto that scratch area.

Awesome. would a poultice take out grout though? i dont think of grout as a stain

It will take the color out of the grout.

Nice spot for a little suction hook to hang a loofah or something. I wouldn’t want to risk making it worse.

try the tiny tool first. be careful because it will scratch the surrounding area. I would protect the other surface by using heavy paper and tape so that only the scratch is visible. this way if it slips, you won't get the good surface. practice on a spare piece first.

I did a little bit of this but got nervous and stepped away. im going to experiment with the white grout and maybe mix with powdered tile as suggested, practicing on a broken tile before i go all the way on this. but it seems like tge best plan. as a side note, the contractor grouted about 1/6 of the shower area on the same day he cemented the tile with versa bond. it doesnt take a pro to know thats wrong. my husband brought it up and the guy said ”oh, it dries fast.” its in an area that wont get hit with much water or traffic, but how worries should i be that the area will fall apart? im pretty pissed.

And it is not quick drying. the bag says to wait 24 hrs for it to cure, in english and spanish, so there is no excuse.

If you have extra tile a good tile guy can easily remove a damaged tile and replace. You might have to sacrifice 2 tiles to get the bad one removed and then replace with 2 new tiles. It doesn't matter that they came on a sheet/mesh.

From what you showed, I don't think I would go through the trouble of replacing. Once you get stuff in the niche, soap scum and hard water stains, you won't notice the crack!