Im not sure how much brick is seen around the window frame, if its only a little brick, you could paint it, although I'd prefer it be a smooth rendered finishor plaster like your other finished walls, because if there are three surfaces visible in there, none will be a feature, and all will look incohessive. To let the ply wall take the focus the plaster is perfect in contrast, so if absolutely necessary, pair. He brick white, although my recommendation is to gy rock and paint, just with he back wall in marine ply. Good luck, I'd love to see your finished result. By the wY, mentioned split battens to hang the ply, if you're unfamiliar, it's where timber battens are cut in half on the diagonal through section, and one half is fixed to the wall, the other the ply sheet, when they go together they become a secure locking fixing. Any handy person or tradesman will know how to do hat, without glueing or messing up the brick wall. It's quick, cheap and secure, and best of all can be removed without much effort to allow you flexibility in time.

Add colour to your room with accessories, then You can change the look whenever you feel like it, without having to paint the walls.

Hi MaxCC, Your 'artwork' is called a wall niche. As far as I know, they were originally used to display religious icons, such as The Virgin Mary. I'm not religious but I do admit that I have a special love for wall niches. I have used them twice in homes that I've built as a place to display my 'Lamplighter' Lladro, so that he is on display to guest. The niches were always placed just inside the front entrance as yours is. Sadly I don't have any photos to show you, as we have just moved house and everything is still in storage. My suggestion, to help you with how to display the object that you will put into your niche, would be to keep the wall itself neutral but paint the niche in a metallic paint. Your want the object on display to be the item of greatest interest and the metallic paint [Resene have some wonderful colours to chose from] will help to draw your eye to that space.

Given your cupboards are Lexicon I’d stick with that either in half or full strength.