Candidate for Flip or Flop!

Greek key trim

Why don't you get white with that Greek key trip in blue or green. that's a relatively easy pattern to find for bathmats.

white or tan

White, with white towels. That's always the answer.

Maybe a dark brown that goes with the cabinets?

Sounds like the bathroom needs to be repainted. The color combo you're describing sounds awful.

Shower and floor is tiled in beige tile, cabinets are a dark chocolate brown, the walls are bluish (the classic 00's blue-brown theme). The walls are a shade of blue/green/grey - so difficult to match. What color would work best for the bathmat? Some neutral that blends into the floor?