As a kid I always knew they must gave painted the background and the moving character separately. Everything that moved gad a different coloring. I always wondered is anyone else noticing that.

Also noticed it! Early computer games hat the same effect for everything you could interact with, purely artistic in that case.

Yeah that was a big hint for the objects you where supposed to look for

Not that much work, really — in fact, Disney streamlined production and often reused material.

I meant the work to develop those methods. Disney pioneered many of them and in many cases had to develop the tooling for the production runs from scratch.