Based on the Compositing and Blending Level 1
multiply : Color -> Color -> Color
The source color is multiplied by the destination color and replaces the destination.
The resultant color is always at least as dark as either the source or destination color. Multiplying any color with black results in black. Multiplying any color with white preserves the original color.
screen : Color -> Color -> Color
Multiplies the complements of the backdrop and source color values, then complements the result.
overlay : Color -> Color -> Color
Multiplies or screens the colors, depending on the backdrop color value.
difference : Color -> Color -> Color
Subtracts the darker of the two constituent colors from the lighter color.
exclusion : Color -> Color -> Color
Produces an effect similar to that of the Difference mode but lower in contrast. Painting with white inverts the backdrop color; painting with black produces no change
hardlight : Color -> Color -> Color
Multiplies or screens the colors, depending on the source color value. The effect is similar to shining a harsh spotlight on the backdrop.
softlight : Color -> Color -> Color
Darkens or lightens the colors, depending on the source color value. The effect is similar to shining a diffused spotlight on the backdrop.
colorBurn : Color -> Color -> Color
Darkens the backdrop color to reflect the source color. Painting with white produces no change.
colorDodge : Color -> Color -> Color
Brightens the backdrop color to reflect the source color. Painting with black produces no changes.
lighten : Color -> Color -> Color
Selects the lighter of the backdrop and source colors.
darken : Color -> Color -> Color
Selects the darker of the backdrop and source colors.