Hehe, its a really useful feature isnt it, I keep a few of each banner in my Enderchest so that all I need is wool at a new build and i can then just copy the banners unto infinity.
I spent a long time in creative going through banner designs, with multi-colour, multi design processes. Place them down in a line in creative and have a look and what you like and dont like, then develop it from there. I'd try to fit in maybe another colour, reverse the colours, or mix it around until you find one thats a good fit