/ic/ - Artwork/Critique

>>6652191
I guess you could call Rocko an early "Silver Age" cartoon, which is when all was still done by hand and digital imagery was incredibly rare and only in feature animated films. A notable change in the industry was the outsourcing to Japan and Korea; animation work used to be handled domestically before. It's likely the BG work was also done there.

These backgrounds would have most likely been done with gouache or watercolors (or acrylic?). If you're concerned with making something "look" trad, you can always use specific brushes, textures, dirty marks, filters and color adjustments. Traditional pigments have a certain color to them, which is why the color of digital anime looks so different from the one on physical cels.

If you're asking about the deeper-level stuff (composition, colors, line quality, aesthetics, light/dark), it's a little more complicated. I don't know any courses for this specific interest, but learning those different facets of painting and drawing would be useful. The other very important skill is an inner sense of design.
I'd reference/copy the backgrounds you like to get a sense of them. I'd also encourage expanding your visual library of animation backgrounds. This could be anything from Walt Disney cartoons, Ralph Bakshi movies, Soviet/ExYu animated shorts, UPA animations and the like. And there's also something neat about the McCracken/Tartakovsky era CN.