Travertine is a soft, limestone material often used for floors, counter tops and bathroom tile. Because it is porous, any grout that gets on the travertine itself, rather than between the tiles, must be wiped away before it dries. If that isn't done, careful measures must be taken to remove the grout and not ruin the travertine.
Use a single-edge razor blade to very gently scrape away any clumps or layers of excess grout on the travertine.
Use the finest grade of steel wool to lightly rub the travertine to remove any excess grout too small to remove with the razor blade.
Remove the remaining film residue with a heavy-duty alkaline cleaner that is rated safe for limestone and travertine (available in hardware stores). Before applying the cleaner to the travertine, test it on an area that won't show to be sure that it won't discolour your particular travertine. Since a variety of sealants are used on travertine, you can't be sure that there won't be an undesirable interaction between the two.
Wash the travertine with warm water and a soft rag. After it dries, buff it with a soft rag to completely remove any grout haze.
Since travertine is porous, some varieties have natural holes and cracks to give the stone character. You may find that excess grout has filled them. The only way to remove such grout is to chip it out with the razor or drill it away using a fine-tipped, hand-held rotary tool. That is difficult to do without further damaging the travertine, so it is usually best to leave that particular excess grout alone.