An interesting pre-production color sketch by Walt Peregoy. As you can see the style is much looser here than the eventual final look of the film. I am not sure if Peregoy thought this should be the look of the production BGs or if he just set the overall color mood in this piece.
Interesting, too, is that Mowgli's poses are from an actual (rotoscoped) scene in the film, which at that time was already animated. To paint his loincloth red instead of white was a smart decision.
Here is another early Peregoy Jungle Book study:
https://andreasdeja.blogspot.com/2014/02/walt-peregoys-jungle-book.html