I like dark statement walls, but I think with your tile selections that it would end up looking too top heavy. Your tiles are light and airy... very nice, but they don't lend themselves to the drama of a dark wall in my opinion. I'm assuming you don't have any natural light in the powder room? You would probably get the best/classiest look from going with a nice, crisp white. Greys can be really hard to look right in rooms without natural light... they want to skew towards blues, greens, purples or whatever color family they are tinted towards. I have used that to my advantage in some rooms that have no natural light, but I was going for that blue color without it feeling overpowering... and it looks like a soft blue, but if you just saw the paint chip in normal daylight you would've thought I chose a plain old grey.
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