I know it would be a LOT of work, but perhaps taking a page out of the model railroader's handbook and making a cover that looks like the top of a coal pile to put over it would be a little more authentic-looking? Or, maybe make some black fiberglass coal to put over what is already there.

A realistic coal pile would only be seen from above -- not the view that most visitors ought to have!

A fake coal pile would have to be 'down' on the sheets, leaving a valley around the outside that would have to be drained (or that would form a kind of crater lake in the caldera of the coal space that would have to be carefully sealed against leaking...)

The fabricated weather covers are carefully made to shed water without possible intrusion. Gluing fake coal to the top of the curved pieces is certainly possible (to give the effect of a coal pile as seen from the ground) but I think it would impede drainage and hold moisture that might accelerate rusting of the new covers -- not to mention that weathered 'coal' material might run down and stain the tender sides.

Yes I think it might be one of the ads that may cause an issue..

For some reason the above posts prior to my last did not show up earlier when I replied??
Overmod hits the nail on the head perfectly. We did consider installing fake coal but it would only compound the water intrusion issues by allowing the water to back up or enter areas it would not normally enter. We are trying to keep the water our completely. I wasn't sure what to do for paint but I think we might go with a matt anti slip type black paint so it doesnt appear she has a roof or looks like an oil fired loco and tender.