You need some foliage to break up all the concrete. Maybe some type of reed grass. Horsetail reed would look very nice because it grows so tall, but you must contain it so it doesn't spread.

I would prefer something that blooms, dependent on where you live, etc. Although it doesn't bloom, I have had good success with dracena marginata. One variety is variegated with pink and white stripes on green. I will look for a photo. Mine are currently over five feet tall, but you don't have to contain them; they grow straight up but have a nice tropical feel. I started out with three 6" pots, planted in a triangle in an 18" pot. You get a lot of bang for your buck with this plant. Easy to grow, virtually no maintenance, modest water requirements.
A little bistro set would be a nice addition to the patio, too.

Hadn't even thought about tall plants - thanks for those ideas! The patio gets almost no direct sun - I will have to take a look and see what would work there.

The first photo is of the pink/white/green variety.
The second photo is a solid green, but shows the plant's mature appearance.
The third photo shows a red-edge green leaf.
Another advantage is that on your patio it will be protected from wind and extremes in temperature.

Dani, direct sun is not required for dracena. It can tolerate sun well but grows quite nicely in primarily shade. Also very resistant to pests. I have never had a pest on any of mine.

If you like a bit of whimsy. . .

Bright outdoor rug. can you paint the walls?

Beautiful! Thank you!

Lady Di (love your name!), I'm thinking a bright glossy white for the walls and maybe some slate deck tiles for the floor. I can't decide on furniture though. Maybe a wrap around bench with storage. I'd love to build one with reclaimed, silverish wood - if anyone has any good diy instructions for a bench box that would be great.

I would use the wall height and do a full wall of tall "bookcases" out of outdoor wood or pallet wood and put potted plants on the shelves…for maximum space use another corners and do square lounges right next to the walls….you can also string lights across the top….

Make YouTube your friend. I love this young lady, she can build anything, How to decorate a small balcony Season 1- Ep 4 by EngineerYourDesign or Exterior Design-DIY Small patio makeover on a budget by House and Home

Are you able to attach planter boxes to the railing? If so, you could plant trailing plants that would add color without using up floor space. Some nice tile on the floor and maybe a weather proof cafe table set.

Reused, unfortunately I can't attach anything to the railings - but I like this idea! Thanks!

Susan and Vstavay - these are great! How did you do this?

You have a small blank canvas to work with! You'd be surprised at how amazing it can turn out to be! Consider also changing the concrete with hardwood deck tiles. In a small space as such it can really give the area an amazing warm natural look. Specially when plants are added.

Below is a job we photographed in Laguna Beach, CA It's a small porch/deck The same concept can be achieved in a much smaller space like yours.

How about a Dine A-Lowha Table 29.5″H x 34.4″W x 34.4″D available Here: Dine A-Lowha

Plus 3 Easer Chairs available here: Easer

Seaser Lounge Chair with a Teaser side table / foot rest