800 years of candle soot on the inside and 200 years of city soot on the outside does tend to darken it quite a bit. At [1] you can see a picture of the Chartres restoration, with the nave complete but the transepts still the old color, which is much darker. (The Chartres restoration gets a lot of hate from people decrying painting over the beautiful "raw stone", but a) the cathedrals were originally painted, and b) the actual stone was hidden under centuries of grime, including from an oil furnace installed in the 1960s, which the restorers painstakingly scraped off. I thought the new surface looked fantastic when I visited.)

[1] https://galliawatch.blogspot.com/2017/05/chartres-restoratio...