“NEGLECTFUL CENTURIES have seen the great churches of the High Middle Ages lose one of their most striking characteristics: color. Traces of pigment reveal that many were once brightly polychromed, both on the interior and on the exterior.”— from the article LIGHT SHOW at AMIENS, at The Lion and the Cardinal.
However, I don't think we ought to believe that the churches were painted so garishly as depicted in the article's photographs. But the church was illuminated by lasers, which tend to produce pure colors, and so subtlety likely cannot be depicted. With such fine stone craftsmanship used in these great churches, undoubtably equally fine painting was also used.
Only recently have scholars determined that the buildings and statuary of classical antiquity were also painted — demolishing centuries of Enlightenment art theory. However, these scholars very much think that the colors were garish and ugly. That can't be true: see my article here.
The famous Gothic revival of the 19th century was based on the mistaken notion that the medieval churches were plain stone; perhaps this false supposition led to the eventual rejection of the Gothic in the 20th century. A new revival of this style will likely be impossible if garish and ugly colors are thought to be "authentic".