these buttons have no effect unless the render plugin passes true for RenderFeature.PostEffects:
tested on windows 8.11.24230.13001, and I am returning true for RenderFeature.RenderChannels
they do work on rhino 7, and they can be tricked into working after rendering on rhino 8, if you switch current renderer to rhino render (or, I suppose, any that returns true for PostEffects) without closing the render window