gray goes good with blue, slate tiles have blue and gray in them. I just bought the new 6x20 wood-look ceramic tiles from Lowes in the dark finish and that would look good too.

You can never go wrong with white. Then you can add any second color you want. Lime green accessories or accents such as a rug or some of this color in your shower curtain would be striking!

I've seen some great "off gray" tiles at our local Home depot...they are pretty cheap too...about $1 per sq foot. I like to use darker grouts so the grout does not get so dirty too quick.

You can never go wrong with neutral colors. Have you thought of ivory color? They are not completely white, but looks more upscale.