Back in the seventies at Disney, animation was hand-drawn line art that was then xeroxed onto acetate. Colors were then hand-painted on the reverse side so that the lines of the art weren't covered and the brush strokes didn't show. This is the reverse side of the Marian Pleads cel, showing the paint process behind the lines and acetate.

When I first took the cel out of its frame and looked at it like this, I had such an odd feeling. Like seeing someone in their underwear or something. >.>