If you're open to painting, I'd go cream and greige on the wall, instead. If you're looking to keep these the same and tie them all together, I'd add accessories and decor that use a lot of natural elements in mixed tans and greys: mixed stones, birch with the bark still on, driftwood or other weathered woods, white-washed or grey-washed rattan or wicker, clear glass with multiple elements inside, etc.

I'd go with bath towels in this color or similar.

SW Perfect Greige

SW Balanced Beige

SW Popular Grey

SW Charcoal Blue

I would paint walls, including the wainscoting, Popular Gray. Style with natural items like baskets, and navy linens.

If you paint, I like the balanced beige.

Love your white batten walls and warm granite countertop.

I love that charcoal blue! that's great!

I would use a light beige or light green on the walls. The dark gray walls look very heavy with the beige countertop. Add artwork in simple gold frames with white matting.

Can you add more photos to show the other walls? Is there space for art? Hand towels?

It's hard to suggest things for a room you can't really see and don't know your style or preferences. Some people really dislike orange, but I'm a big fan of certain shades of it and think it would look great in your room; same with teal. Teal and orange together? I'd add wall art and not junk up your counter with unnecessary stuff/decor

Hi, Daniel, you asked about accessories. I think black and gold accessories would look stunning in your bathroom.

2 sets of towels if this is a full bath

http://www.walmart.com/ip/Derry-Solid-Egyptian-Cotton-Bath-Towels-6-Piece-Towel-Set-by-Impressions/35683835

Or set of Turkish cotton hand towels if this is a 1/2 bath. If you like the feel of microfiber, here are a few

If this is a 1/2 bath, a bath mat isn’t a necessity, but would be for a full bath. Your floor isn’t in the photo, but this graphite gray would work with your gray wall paint and white board and batten.

If you need a gray to corral items, like comb, hand lotion, etc, a narrow tray would fit on the counter over the toilet

*tray not gray

Individually, all of these elements are lovely. I love the grey paint next to the white batten wall but honestly, the countertop color and style clashes with everything else. It’s like two opposing styles collided. While changing the grey could improve the color flow, I still think I that the granite lacks unity with the batten, sink and wood framed mirror. If you‘re open to changing the countertop, I would opt for white marble or white quartz. Plain white porcelain would also work. Keeping it clean and simple will tie in the entire look. Alternatively, if the countertop must stay, I would change the paint and (sorry) remove the batten.

I think he wants suggestions for decorating, not painting... I agree with Kate Hip. Look for art that ties in the browns of the granite, etc. Not sure what other things you're looking for. You could pick an accent too, like a green that could appear in rugs, drinking cup, etc...