Check this post:

http://ths.gardenweb.com/forums/load/kitchbath/msg120415217214.html?19

theresse had the same question that needed answering immediately (yesterday), made a choice and I think she didn't like her choice. There may be another post about what she may do about that.

I think the best advice she got, which she couldn't follow because of the time constraints, was to grout sample pieces and see she what you like.

A white grout to match the white of the carrara. Tight grout lines 1/16". Will give you a classic look.

My only caution about white grout on the floor is that it will get dirty. Try to pick out a medium gray from the marble and match that.

Homechef,pharaoh & Suzannesl, thank you for responding. I think Suzannesl's suggestion about trying out different samples might be my best bet.

Look at Laticrete's Silver Shadow.

Thanks Bill, that looks really good, I'll try and sample that one.

We used delorean gray and I just posted the pictures a few minutes ago. I think it is darker than you want though.

Gryane,
I would love to see photos. Platinum is my first choice, but I guess I've been second guessing myself.

Platinum would look pretty much the same as the silver shadow. Just two different companies.

Thanks Bill, I'll try to get a sample of both.

Here is my carrera shower with platinum grout. I hope you can see clear enough. the lighting is not that bright in there right now.

Thanks gryane,your shower is stunning!! I think platinum is the best choice for me.

Gryane, one more question. Is your platinum grout made by Polyblend?

Gorgeous, Bill! Looks like you're right on with the color!