When is a shoot-em-up not a shoot-em-up? Erm... when it's a paint-em-up, of course!
ChromaGun is a color-based first person puzzler. The player shoots walls and droids to colorize them and droids are attracted to walls of the same color. The challenge is to mix colors and to try getting the WorkerDroids to work for you – instead of killing you.
I love the idea, check it out on Steam - at the time of the posting this, it's 15% off the normal price. Released last Tuesday (16th February 2016) by the wonderfully named Pixel Maniacs. Available for PC and Mac.