We love a good tone-on-tone look. Plus with the wide range of greys, you can choose a light grey couch and a dark grey floor and vice versa. Or choose a couch in the same color as your floor for a very contemporary monochromatic look.
Grey tends to have a lot of blue in it. So blue is a natural color to pair with grey flooring. We love a navy couch with a mid-tone grey floor. Or a soft turquoise paired with a dove grey. There are dozens of ways to mix up a blue sofa and grey flooring.
If you're not worried about stains or spills, don't have a big hairy dog, and love a bright and light atmosphere, then consider a white couch. They look super with all colors of grey flooring and work within many different decorating styles.
Pink and grey are a super fun color combination. It's flirty and fresh and is a super distinct look. A pink sofa may not be for everyone but it most definitely works fantastic with the color grey on your floors.
Here's another distinct combo. Yellow and grey have kind of an urban vibe that is city loft cool. Whether you go for rich goldenrod or something as pale as wheat, you won't go wrong choosing a yellow couch for your grey floor.