I would add a hunged glass shower screen and then add some color with art on the wall towels in a color from the art an a nice fluffy colored bahmat

This is such a neutral room that you can really add most any color to it. Find a shower curtain you love then add towels that complement it. OR - Hand a piece of art you love above the shelf over the toilet. Pull colors from that for your shower curtain and towels.

I personally am a fan of monochrome so I'd probably add a simple shower curtain with dark grey trim and very dark grey towels. But, I realize most people want more pow.

For right now I would pick a colorful shower curtain that goes well with the agreeable gray, then get towels, bath mat, art/décor that works with the shower curtain.

After you have been in your home for a bit and have decided on a whole home color palette your day 1 decisions won't box you into a design decision that you have not had time to fully develop.

Since I know nothing about your taste, I can't make a guess at what types of patterns or styles you like but you can see here how many colors work with Agreeable gray.

Not much needed, depending you your style. A few accessories, white waffle weave shower curtain, white towels, wicker waste basket, vintage mat are one of many ideas...

Or something colourful...

I'm another vote for a shower curtain you really like to look at (I love the one Jennifer Hogan posted!) and then simple colored accessories to match. You won't be using it a ton, so let the neutrals help you out by staying out of the way.

Sometimes a space doesn't need color, but contrast. The drama of charcoal gray walls and a patterned shower curtain could be a great start.

You might try adding pops of color with artwork and a plant. You could easily just do a white shower curtain and white towels to keep it clean and simple. Note our two bathroom designs below:

Wine Country Charm · More Info

Sophisticated Luxury · More Info

You might try some artwork, colorful rugs, a patterned shower curtain, a plant or two, and some colored towels. Here are just some ideas for you from some bathrooms we have done.

Oceanfront Oasis · More Info

Front & York · More Info

West Side Whereabouts · More Info

Where is the flower are from in the photo?