Color Advice for Bathroom Towels?

With grey as your background, you can pretty much go with just about any colour that you want (except perhaps browns or oranges). I would choose a shower curtain first, in a pattern that you like, and then choose two (or three) colours of towels that match. I go with the shower curtain first because it is more difficult to find something that you like in a curtain. I have a white bathroom, but the colours I have (which would work with your room) are burgundy and dark green.

In your grey room, you could go with white, black, and grey, or a dark and light shade of a colour you like such as green, pink, purple, or blue, with white for a third colour if you need a lot of towels in the room. Red, white and grey, or two colours of grey and a fairly bold accent colour such as pink or red. Really, you have a lots of choices.