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
convention.
Example with separate specular highlights rendered
{F7626679}
Old rendering method (`shaded_color = (diffuse_light + specular_light) * base_color`)
{F7626708}
Comparison with new method
{F7626707}
Example matcaps for reference/testing
{F7626685} {F7626684}