See flutter/website#9362.

The native renderer, at HEAD, currently dithers all gradients in both Impeller and Skia. While this is configurable via the static app-wide flag Paint.enableDithering, in the near future it will not, and we'll merely always dither gradients, and never dither anything else.

I took a quick look at CkPaint, SurfacePaint and SkwasmPaint, and don't think the web engine is every referencing Paint.enableDithering; in other words my changes have had and will continue to have no effect. I'm also not sure if there is a way to do conditionally dithering or if gradient banding issues occur on the web.

For now I'm going to mention this feature excludes the web rendering engines.

If that's WAI and there is no way to do this properly, feel free to close the issue!