I've been working on an existing Apple II emulator, OpenEmulator, which takes an interesting (and as far as I know, unique in the Apple II emulator world) approach: it renders a fairly raw NTSC-like signal, and then uses GPU shaders to convert to colors, while adding fairly realistic CRT effects, like persistence, curvature, dot masks, etc.

The result is an emulation that is incredibly close to what I see when I walk downstairs and run my test code on the real Apple IIe in my basement. I guess that's what happens when a DSP person writes an emulator :-) (The original author has disappeared themselves from the internet, unfortunately.)