You have come to the right place! Tenax travertine filler is actually used in approximately 75% of the filled slabs in the world! This is a resin based product that is semi-solid( that means the consistency is between a flowing and a knife grade consistency). It is already colored a buff color (some call it a cream color) to match travertine.
You just mix it with the hardener (which is provided) and trowel it in (if the stone is very soft use a plastic putty knife. It will dry very quickly and matches travertine very well. You can even make it shine by buffing it with extra fine steel wool (or you can scuff it up with extra coarse steel wool). Cleanup is simple - use a rag with some denatured alcohol.
Here is the link:
http://www.defusco.com/glues-epoxy-polyester-etc-tenax-travertine-filler-c-82_506.html?osCsid=4706a4227dd2e725960271cffbd146faGlad to be of service,
Mark