(Thank you Professor Nina Willburger @DrNWillburger for bringing this article to our attention.) Most of us assume that the white marble in ancient Rome was painted to give the city its vibrant colors. I hadn’t considered the use of colored marble, either:       https://www.heritagedaily.com/2021/05/analysis-of-wall-decoration-dating-to-the-second-century-a-d-provides-new-insights-into-marble-extraction-and-processing/139172?fbclid=IwAR0Rg8oAX9TJwZGR4oEBK2-eUYajwweZ