I disagree re tan and gray not working together. There are warm grays and cool grays and either will play very nicely with tan. Just think of a beach — sand and rocks (and skies) — a full spectrum of grays and tans, from palest of tan to golden to blue gray to dark charcoal. Nature proves it's a wonderful combination. Perhaps think of your bath as that backdrop, and add interest and contrast with some hits of more intense or saturated colors, e.g., deep grayed-blues, seaweed green, etc. You could even look at a mussel shell for how that whole warm plus cool palette comes together so beautifully.