Multiply
Multiply:
base layer x blend layer
luminance values
Multiply combines the color values of both layers, which has a darkening effect. The lightest values in either layer become transparent, which makes it very useful for coloring in lineart, removing white backgrounds, and shading. In the example below, reversing the layer order doesn't change the result, but in most cases lineart and shading will be on the blend layer, and colors on the base layer.