The color travertine you used is a pretty common color.
Travertine tile grout color.
If you re wanting to contrast and go darker as patrick has suggested i would use 59 saddle brown.
Iranian travertine offers light golden brown and cool light mocha brown.
Travertine has a pitted mottled texture layering and an even light beige color.
Noce is a travertine with a delightful caramel brown color.
Other than the meek color it s not for the design faint of heart.
Unfortunately in this case it sounds like the darker grout did absorb into the travertine tiles and stained the travertine.
Grout in a darker color can be chosen to fill the holes and lines for contrast.
It s a stone that gives your kitchen or bathroom backsplash floor or bath shower walls or surrounds an ancient roman look.
It is advisable to seal travertine tile prior to grouting when using a darker colored grout.
Both warm and cool and light and dark shades are found.
This is particularly true for a rougher tumbled finish.
More information about this product.
I use custom building products grouts 122 linen would be great product to blend with.
There are many shades of brown available in travertine.
Travertine is more about texture than it is about wild coloration.