Workbench multiplies the colors of painting modes on top of the current matcap, which affects the final color of the surface depending on the color of the matcap. The more accurate way to work with colors is using flat shading, but this mode does not give any information about the volume and shape of the surface.
In order to fix this, we should include a way of rendering the mesh surface as white as possible while showing the volume. A possible solution would be a matcap like this (it is far from perfect, just for testing):
{F8657377}
{F8657386}
Current Default Studio Light/Flat Colors
{F8657441}
Proposed Matcap/Flat Colors
{F8657448}