I'm quite sure you could change system colors willy nilly in OS 8. It was great fun. I miss that part - the feeling of having "your own" system.
Since customization where pretty standard back then, it feels like product managers pushing their "vision" rather than technical difficulties preventing that nowadays.
Kaleidoscope and later on Appearance Manager in Classic Mac OS were so much fun. No OS theming system I’ve encountered since have been as capable as those were.
Ye I wonder what fantastic APIs were actually exposed. I remember some 3rd party screen saver I had. Where like Goofy peeked out of folders and Donald Duck was cleaning up some file mess. I mean, how could you even program that?
I think it was on the real desktop, not some bitmap, but not too sure.
Since customization where pretty standard back then, it feels like product managers pushing their "vision" rather than technical difficulties preventing that nowadays.