Which do you prefer - highlight or matching? We have similar porcelain tile, although more gray than greige, and we wanted the grout lines to disappear as much as possible. We used Tec Power Grout in ''mist''.

Here's a pic without the flash:

And this is a little more true to color on my monitor with flash):

The best advice we got was to place the plastic grout sample between the tiles with them on the floor and look at it that way.

We also had out tile guy do a sample for us, which helped.
(sorry if the pics are gihugic-photobucket is out to lunch for editing this morning, I guess)