I have always had these issues with macOS attempts on this machine. Basically it looks like the display is in 6 bit color or something. If I display a gradient on the screen it is not choppy, and the colors do not look as good as normal. Especially when I open up the Spotlight Search, the shadow behind the window has what looks like very visible contour lines behind it, so maybe some kind of alpha thing.
I have always had these issues with macOS attempts on this machine. Basically it looks like the display is in 6 bit color or something. If I display a gradient on the screen it is not choppy, and the colors do not look as good as normal. Especially when I open up the Spotlight Search, the shadow behind the window has what looks like very visible contour lines behind it, so maybe some kind of alpha thing.