Ok, it is taking me some time to think through the implications of this change. It is obvious that this fixes a real problem, so that is a definite plus. My main problem is that these new methods are still not defined in the classes, so only artists that go through this conversion processes (admittedly, that is most of them) will get these special methods defined. This will cause confusion for users, as well as the maintainers because debugging will be harder to do.

If you are looking to avoid duplicating code, you are free to make a private mixin class_Color3DCollection that has these methods properly defined, and have Poly3DCollection and Patch3DCollection inherit it. Or just duplicate the code, it isn't all that much there.

@WeatherGod looks like Poly3DCollection was already fixed years ago. should I change it to make the style unified?

I believe this was superseded by#18189 so I'm closing, but feel free to re-open. Sorry@xiaoshiqi that this never got in, and thanks for your efforts.