You can see a contrast in pictures of the Chartres restoration. See [1], 5th picture down. The light areas are the restored, painted areas (if I remember correctly, they carefully scraped off the grime with scalpels to reveal the original paint, although I don't know if they did that for the whole surface or just used that information to scrape it off and repaint it). The dark areas are the unrestored areas.

After 900 years of smoke from burning candles, and an oil furnace in the 20th century, the surface got pretty dark. The restoration was controversial because some people thought that we should either keep the "patina of age" or they thought that the patina was the natural color of the stone.

[1] https://francetoday.com/culture/chartres-the-famous-cathedra...