Mark

I find HVS is a much more intuitive color model for mixing colors. You drag the hue slider left or right along the rainbow colors to determine the primary color then you drag the value and saturation slider around inside the large preview box to establish light and dark and more color saturation or less color saturation.

Various applications try to replicate a specific color in CMYK using different algorithms. They all basically come up with the same results but by different methods. So one application might use more black to make a color denser and another might use a higher percentage of the three primaries CMY to make a color denser. In the end the two color may print identically, but the mixes are different. So the answer is no set rule for how a program mixes a certain color.

The exception to this is the Pantone libraries which should be the same from one application to another because this is a universal palette using a specific formulation.