Sometimes (often) it's the simple ideas that can have a big impact in a room. Years ago, I did this block painting project over a fireplace. Using all sorts of leftover paint in the garage, I mixed yellow, white and beige to my hearts content, ending up with 8 colors (I think).
Then I took a level, pencil and painters tape and just outlined squares and rectangles. The key here is to label each cup of mixed paint and make yourself a little diagram of where each color is. You'll need to do two coats, and believe me, you will NEVER remember which square is which cup of paint. No mistakes can really be made though. When it was all done, I put a lovely framed landscape on the mantel.
I will always love this project. It could go behind a headboard in a bedroom, on a plain, cheapo closet door, on a small wall in a dark hallway, around the mirror in a bathroom. You could use any color combination that makes you happy, but I think part of my success here was that it was very tonal. All one color family.
Give it a try. Easy peasy.