How do I blend colors in a natural way?

[peterm87530620]

I'm looking for a way to naturally mix colors while painting in Photoshop.

I've attached a picture that shows what I'm looking for (the one that says 'Natural Colors On')- it was created using Escape Motions painting program Rebelle 4.

[Norman Sanders]

The term “natural” has me stymied because the example is a typical subtractive color overprint with a special color applied in place of usual cyan. As a result, the green you were expecting was not produced. A straight overprint of your transparent colors cannot produce green (assuming white paper and white light illumination).    

In my example above in CMYK mode (ink or paint white paper), the layers are set to Blending Mode: Multiply. With a proper cyan applied to the yellow, green was produced.

Imagine for a moment that transparent ink or paint is a color filter and that white paper reflects red, green and blue light in approximately equal amounts. In other words R+G+B =W. That is an additive system. We begin with blackness and add light to produce white light. 

When you paint or print on white paper, you begin with white and each transparent paint color acts as a filter that allows only part of the RGB to be reflected. A subtractive system.

Cyan allows the Blue and Green light to be reflected.

Magenta allows the Red and Blue light to be reflected.

Yellow allows Red and Green light to be reflected.

In your case a color other than Cyan was used, so rich Green is not in the cards. The wrong "filter" was used. 

The “Natural” sample is impossible without additional manipulation.

[EDIT] Perhaps this illustration will clarify additive and subtractive color.