I totally agree with painting one wall yellow/orange and the others in white. A good choice would also be honey yellow or terra. I guess when people hear orange they freak out because they probably think about neon orange or something too bright and disturbing for the eyes. How about mint? This is quite a popular color this days.

I feel like the art above the water cooler is too much to the right. I would move it a little more to the left. But if you have the ability, I would actually replace it will a picture or painting that is not two dimensional. In other words, a picture where your eye can wonder as if it was three dimension. Maybe a simple beach scene or mountain scene. Something that suggests space since the room is quite snug.

Something like silver birch trees don't take up too much room but will provide some height and interest. Personally I pick out natives, after asking local garden centres for those which are natural to my area. I've used black mondo grass across the front of my walls with purple fountain grass behind it. The fountain grass really takes the summer heat, doesn't need much water and self-seeds. It's grown slightly taller than me after a few years. I have, what I call a 'survival of the fittest' garden. Over the years, I've experimented with all sorts of plants. Eventually, only those that survive with little help, and almost no extraneous watering, get to stay. One of the key things I did when planting out my garden was to dig down into the soil and lay a mat of used, natural-blend carpet underlay (not the more synthetic types used these days). Just ask someone getting rid of their old carpet- it's easy to come across. Above the carpet underlay I added water crystals, then put the soil back on top. After the gardens have been established, I haven't need to get the hose out since. I do have lots of succulents around the place, some native plants and ornamental grasses. I hope this helps.

Had you considered reconfiguring and adding to the pool fence in order to incorporate the pergola inside pool fence boundary? I can certainly understand there are pros and cons to this, but I thought I would throw it out there. In any case, landscaping, lighting and painting pergola a more harmonious colour seem very good ideas to me. If you sketch out on paper some of the various plans and ideas you like or have in mind, and colour-in the different features, this might help you visualise things better. It's sort of rudimentary, but I have done it several times and it did help me 'see'. Best wishes, and please keep us posted on how you are going.