The blue is a nice color, but its fighting the yellow tones in the tiles. I'd use the colors in the tile border as your guide. Consider using the tile border colors, pick one and then either go lighter or darker than the border color you pick.

'you want to make it look more gray as the rest of the house is". why? why does it have to be gray? you have a travertine w/very warm yellow/beige/peach tones. why do you want to force a color on it that isn't the best? forget gray. At least any of the blue grays.

try SeaSalt, or a soft sage, or Pale Oak, or soft tan tone.

No paint color is going to make travertine look gray. Embrace the warmth of travertine, and use softer bluegreens like Beth suggested

I agree with the others here, you're not going to be able to do a gray and have it work well. I'd go with a soft, creamy off-white and do the trim in a wood tone (medium brownish)