My native language is not English, so this article may have some incomprehensibility, I will try to explain. And I have read the precautions, but I may offend if the language is not clear, I sincerely apologize.
The mixer brush in photoshop is used by many people because it is close to oil painting to a certain extent. I tried to simulate this effect, but when the Color Rate is high, the smear function cannot be performed at the same time, and the bottom color will be covered.
It should be cumbersome to copy this function completely, and a new brush engine may be needed.
Perhaps we can refer to clipstudiospaint to make some modifications to the Color Smudge Brush to achieve the effect: the two color mixing modes of csp are very similar to krita’s Smearing and Dulling, but its color rate is divided into two, rgb and opacity. When the latter is high and the former is low, the effect of color rate and application can be maintained at the same time
I made a comparison between krita and csp (because there is no ps), only when the color is dim, the application of krita will take effect