Difference Mode: Okay, if you’ve been following along so far, this one might be the one that throws you. Difference compares the blend color to the base color, and subtracts each from the other based on their value to arrive at the result color. Confused? To demonstrate, make a red brush stroke in Difference mode (either set the paint mode to difference and paint on the same layer, or use a normal mode brush on several Difference layers). Then cross it with another. Next, scribble over these with a blue paint brush. The result keeps changing, but not in the same way that it would in Screen or Multiply modes. If you go over the whole thing with white, the result is the same as though you had inverted the color (Image>Adjust>Invert).
Exclusion Mode: Similar to Difference mode, but not quite as high intensity.
Hue Mode: Hue won’t change the brightness value of the base color, or its saturation, but will modify the pixels toward the blend color (as close as it can get while maintaining value and saturation of base color). Hue mode won’t modify black, white or desaturated (gray) pixels.
Saturation Mode: This mode works like Hue mode, only it leaves the hue and value of the base color, while bringing the saturation of the result color more toward that of the blend color. Saturation mode won’t modify black, white or desaturated (gray) pixels.
Hue and Saturation really need to be seen to be understood. I recommend scribbling on a new document with a couple of different colors. Use the HSB color sliders and see what happens when you paint over a high saturation red with a low saturation blue in hue mode. The blue will match the high saturation of the red. Try destaturating the entire document (Image>Adjust>Desaturate) and then keep experimenting with the Hue and Saturation modes. You’ll notice that painted areas of your document no longer accept changes in these modes.
Color Mode: Similar to the above modes, except color mode will change the base color to the hue and saturation of the blend color while maintaining the value. If you had a grayscale picture and painted over it in Color mode, you would change the hue, but not the value of the original image.
Luminosity Mode: This mode is an inverse of the color mode. It uses the blend color to establish value while preserving the hue and saturation of the base color.
Article by Seth Rogers.
