Yes, there is no reason why the panels can't have decoration on them like the ones on the Overground Stations. These haven't been been covered in graffiti (infact many underpasses that have decoration on don't).

The I believe enamel panels for those stations were made in London (we used the company that makes the Underground enamel signs when we designed the signage for Billings in Sydenham).

The question is, what should the graphics be? I'm sure if you get together you can influence what you will get.