Any color but white, grey or tan (beige). Brighten up that monochromatic look. Have some fun here. Fun is better than classy! (I'm not sure I even know what "classy" is. So far "classy" looks like dull to me.)

Lighten up - these are only towels. If you get tired of them, you can easily update your look by changing towels.

fuzzy wuzzy

Deep green with a little blue in it....kind of matching the green glass shelf. What makes sense with what's outside the bathroom? Almost any color would work.

No i dont really like deep green as in the color of that shelf is barely noticeable and it being such a small bathroom id prefer a lighter color.

Something to complement the vanity color, maybe a light jade green? How about a printed pattern? If you can find a grey patterned towel you like it would be classy with a little something "extra".