Multiply combines the colors you are painting with the layer underneath, resulting in a darker color. It is one of the most commonly recommended blending modes for painting shadows.
The Math
The color values of the Multiply layer are multiplied with the corresponding values of the base layer pixel by pixel. Because the values are scaled to a range between 0 and 1 before multiplying, the result can only get darker (or stay the same).
Mathier Math
RGB values are normally stored as numbers from 0 to 255, but Multiply first converts those values to a range from 0 to 1. It then multiplies the corresponding values from the two layers:
Result = Top Layer × Base Layer
For example, if a channel has a value of 200 on the top layer and 150 on the base layer:
200 ÷ 255 = 0.78
150 ÷ 255 = 0.59
Then:
0.78 × 0.59 = 0.46
Converting that back to the 0–255 range gives approximately 117.
Because multiplying two numbers between 0 and 1 can never produce a larger number than either input, the result can only get darker (or stay the same).
And that’s why white disappears: 1 × anything = that same value.
And black wins: 0 × anything = 0.
Core Rules of Multiply Mode
White disappears: Pure white has the highest possible value, so multiplying by white leaves the base color unchanged. Painting with white on a Multiply layer has no visible effect.
Black wins: Pure black has the lowest possible value, so multiplying by black always produces black.
Colors multiply together: Unlike Darken, which simply picks the lower value from each RGB channel, Multiply combines the two colors. This creates a darker, blended version of the colors rather than simply choosing whichever one is darker.
When to Use It
Use lighter, less saturated tones: Avoid very dark or heavily saturated colors for your shadow layer. Multiply can intensify them quickly, resulting in shadows that look muddy or overly harsh.
Clip to the layer below: Create your Multiply layer directly above your flat color layer and use Clip to Layer Below to keep your shadows inside the character or object.
Control opacity: Lower the layer opacity if the shadows feel too strong for the lighting you are trying to create.