New in v1.5.0 is surface color smoothing. The following image shows no surface color smoothing:

The following image shows the surface color smoothing enabled:

Turn on surface color smoothing

set surface_color_smoothing

Adjust the threshold: default 0.05

set surface_color_smoothing_threshold, 0.2

frag thr
set surface_quality, 3
as surface
orient

Now pause and look at the surface, especially where two colors meet. Now apply the following settings:

set surface_color_smoothing_threshold, 0.2
set surface_color_smoothing