Sam...Deco for what...are you turning into living space?
You could paint it with various colors in a modern vibe or get a giant mural and attach with ModPodge, then with a razor knife cut through the mural where the garage door sections hinge. The garage door will still function well and when closed the cut areas will barely show. Also you could use stencils of your choice. If you're artistic you could paint any number of designs on it such as green plants or tree trunks, etc. It seems it could be a fantastic and fun project. Maybe even wallpaper the different sections. Great idea to try to dress it up a bit. I hope you will share what you decide to do with us here on Hometalk.
I would try to make it look as if the door was open. Practice on cardboard first to get the hang of it. And if you make mistakes, so what? It's just paint. I like the idea of trying to trick people into believing the door is wide open. Have fun with it.