Dang, that effect is incredible.
Now, though, you've "done it."
The acanthus leaves of the capitals of Corinthian columns were often guilded, and the shafts, too, and in colors many would consider garish.
So, a person could be able to put a heavilly worn red or blue in the "flutes" of the columns.
The leaves could be washed bronze, but with bright green verdigris--and all of the above heavily worn away by time and tide.
It's a way to introduce additional color in a subject, much like color matting a picture.