NSN writes:

You could also use clear epoxy mixed with dust ground off a scrap tile.
But that may wear differently than the original stone and likely show
later.

There is an epoxy ( real epoxy with catalyst) that is made for this
purpose and is the color of travertine. I know this for a fact since I
have some.

You'll get a better color match (and better price) mixing your own. There
are many shades of travertine, not one color. The epoxy cement isn't any
different.