Ken Anderson and background painter Al Dempster had something to do with these color studies for the Jungle Book. The beautiful cel above of Mowgli and Bagheera is a Milt Kahl drawing.
There are endless ways to portray the Indian Jungle, including this early version by color stylist Walt Peregoy:
As you know, Walt Disney opted for a light, airy jungle, since the story included mostly comedic sequences. Dark, mysterious backgrounds would have worked for a more dramatic story treatment.