As far as I know, krita would be the first and only Artist software to have this, if it might be implemented (hopefully):
A color palette in the way a physical palette works.
A white dashboard outside of the painting, where one can paint with a color, the another, then another,
- where one can smear and mix those colors and where one can choose the right blend of color for the brush.
This way experimenting is easier without the necessity of using the main window (drawing) for this.
Also it helps to keep the palette always visible and close by.
Like a second document, just for color mixing - for the main document (the drawing) - so,
that real mixing with smear brushes and whitener/darkener/colors can be simulated.

It's been in the bugtracker for a small eternity, we just don't have someone to work on it: https://bugs.kde.org/show_bug.cgi?id=328487