Thanks for your interest in Sean Michael Design. I don't see why you can't do a grey and black wall color with a dark brown floor, as long as the grain in your wood isn't overly busy to draw attention away from the stripes. Dark brown, grey and black are all neutrals in my opinion...and they all work together (I do grey walls with dark brown floors quite often). Just ask yourself a few questions: Would this work and make sense with the rest of your home's colors? Your final product will be dark and moody...is that the look you're hoping to achieve? Are you going to keep it fresh by using some lighter furniture in the space (as opposed to dark furniture on dark floors and dark walls)? Good luck, and I hope I helped.