I gave it a couple of oil stains. The first a mix of black and green and blue, to make panels lines pop and give it some underwater staining (algae and the like).
And then a lighter one. A mix of white with a little black and brown to mimic ocean floor sediments (also nice to bring out the details on this slightly dark color scheme...
anyway here's the pic of the final result.
The conditions weren't great for photography (I need to buy better lamps or a flash or something) so these are slightly photoshopped... you have been warned.