When you want to mix colors on the canvas you need to use a low flow, and anything the layer modes can do can be created without the layer modes. There is also brush modes that has more than what the layer modes, like Color brush mode is very useful to change the color after something is painted. It will fill in transparent areas, and not something you would want to do. If you mix colors on the canvas, then there are more primary colors you might need to add. Primary colors go like this Red, Yellow, Green, and Blue. You can not skip over green to mix blue and yellow, because traditionally that would make green and primary color are colors you can't mix. You can't mix and get green. If your flow is kind of high, the paint wants to replace the color, and not mix with it. With a low flow you van mix color, but they will be influenced with anything under the colors unless the base color is filled 100%, then you can use a low flow to add color to it for a mix. Like skin color, and redness of the skin, like a sore spot, or light passing though an ear, showing the blood in the ear as if glows. If you'd like to blend two colors together in general, in a more paint like manner, I recommend experimenting with the mixer brush available in newer versions of Photoshop.
