I expect the Deeping Wall, the Burg itself and Orthanc to be dark, nearly black if not black; given the descriptions in the books. Orthanc, in particular, have me thinking of obsidian or basaltic rock (volcanic ... something the Numenorians would have been very familiar with and thus, their descendants who had been in ME from the middle of the Second Age as well as the descendants of the Exiles at the end of the Second Age/beginning of the Third).
"No sadder words of tongue or pen are the words: 'Might have been'." -- John Greenleaf Whittier
"Do or do not. There is no try." -- Yoda
On planet Earth, there is a try.
Indeed, in a world and life full of change, the only constant is human nature (A is A, after all :P).
We old vets need to keep in mind those who come after us.