Sure you can just leave your iPhone 7 Plus without a case but if you want to give it a more unique and personalized look then a case like this is what you want.
This iPhone case has a black background but on that, in bright colors you can find a fractal pattern that kinda looks like a flower (to me). The case is made for the 7 Plus so all the ports are accessible and no hole for a headphone jack but lots of room for the camera.
You can get this iPhone case in a glossy or matte finish.
Come take a better look at this iPhone 7 Plus Fractal Pattern Case.