Add some light up speakers and they dress up the plain panel considerably. Or just add a speaker insert of a ripleys image.
Sometimes less is more in these cases.
Quoted from CoolCatPinball:So, on my new RBION, the plain flat black speaker cover bugs me. I'm thinking of buying a spare and painting it a color that flows better with the rest of the game. Another idea would be to print off some vintage ripleys images from the Web and apply them to the panel sort of like the art on the side of the cabinet, then clear the whole thing. Or even print off one large Ripleys logo, and "wrap" the panel. Suggestions? Comments? Better ideas?