Since almost all of this episode took place inside Twilight’s library, you can clearly see the color scheme and when the lighting changed. The first dark bluish stripe is when Twilight’s telling her ghost story, and the second, broader purplish stripe is when Rarity and Applejack are arguing in bed. The big greenish blotch is when the tree top crashed into the library afterward.
Wow that bit with the tree at the end is like 1/6’th or 1/7’th of the episode.