Get an indoor outdoor area rug for the couch area and a few couch pillows to compliment the rug,a woven coffee table you can merchandise and a large living plant for those beautiful windows and you're good to go.

If it were mine, I'd paint the ceiling and wood trim white, and I'd paint the rattan on the furniture in a color. And yes, paint that strip of wall, unless you go with a green theme.

What's under the carpeting? I'd pull that up and put a large indoor/outdoor rug down.

then a couple of pillows with color and nice but simple patterns for the sofa.

I'd start with pillows and rug and colorful accessories. Consider Paint stamping a design on the curtains with bright colors. Paint the strip above the windows then see where you are. What a nice room!

Lots of plants, colorful pillows and a coffee table.

I was going to say something similar to Joanie. Stencil a pattern on the panels and toss pillows. That would be the least expensive way to add color. Shop a thrift store or your house for colorful decorative accessories. I agree with adding some plants too. Flowering plants would be another way to add color.
I personally would not paint the wood.