Get a floor lamp to "warm" up the fluorescent light. Something with a white shade so it diffuses the light.

And, of course, large art. If your budget is tight, consider framed posters - preferably a brown wood frame (to also warm up the space). What is your style? Modern? Classic? Landscapes? .....?

One type of poster I particularly love are vintage event posters, like for museum exhibits or festivals.

Paint it a color you love. Add plants and artwork. Add a lamp to the desk.

Would paint be allowed? This looks like a corporate office. I'm guessing it's not in a home.

Plants are a good idea, you'll need one that can thrive under fluorescent light.

peel & stick wall papers are fun. For something quick, cheap, and moveable, I'd find a large stretched canvas icanvas.com

I had a gray office a few years with no windows - pretty sure it was a supply closet at some point lol - I searched for large-format inexpensive art and especially tapestries since they don't need a frame (both paper and fabric formats) - there are lots of fun options at Etsy, Urban Outfitters and Anthropologie - there are some great things out there that could help fill that large wall

I used to always have a large landscape painting on the wall across from the desk so that's what I saw when I looked up. It was mine and when I changed jobs I took it with me. You could also bring in a lamp as one of the other posters mentioned.

I always added my own lighting to my offices; made them feel so much better. With today's LEDs offering more of a "daylight" ambiance, that's what I'd do (3500-4000K LEDs.) Turn off the ceiling fixture once you have alternative light. Or replace the florescent tubes with daylight LED ones. Pick up the blue from the carpet in a piece of art and some accessories for your desk. Float the desk away from the wall a bit so you don't feel so boxed in by it. If cords go to the wall from there, you can camouflage them with a faux palm plant in a pot that picks up your blue again. Plants bring life to any space.

Art, travel posters, removable wallpaper.

Buy a $20 philodendron that will live in low lighting or a $15 orchid that you can take home after it finishes blooming in two or three months.

A hanger for your door would be good for your jacket.

If you have visitors to your office, requisition a decent chair that isn't gray. If you have 2-person conferences, requisition a pair of chairs and small table in between.

Thanks so much! I wish I could paint, definitely would make it easier!