With Blender 2.80 we introduced a more flexible matcap system. One
change we did was to multiply the matcap with the base color that was
shaded. As matcaps contains diffuse and specular lighting in a single
texture this lead to rendering artifacts. Artists were complaining that
everything looked to metalic.
We now have the option to have a separate diffuse and specular
texture for matcaps.
shaded_color = diffuse_light * base_color + specular_light
For matcaps to support this feature they need to be multilayer openexr
files with 2 renderpasses (diffuse and specular). In the future we can
change this to first pass/second pass in stead of this naming
Example with separate specular highlights rendered
Example matcaps for reference/testing
File used for creating these matcap files