Material Editor > Maps rollout > Click a Map button. > Material/Map Browser > RGB Multiply
The RGB Multiply map is typically used for bump maps, where you might want to combine two maps to achieve the correct result.
This map combines two maps by multiplying their RGB values. For each pixel, the red of one map is multiplied times the red of the second map, the blue times the blue, and the green times the green.
If the maps have alpha channels, RGB Multiply can output either map's alpha channel, or a new alpha channel created by multiplying the alpha channel values of the two maps.
You can also make one of the maps a solid color. This tints the other map.
Color #1, Color #2—Click a map button to assign one of the maps. The check box disables or enables the map. To tint one of the maps, turn off the other map and click its color swatch to choose the tint color, using the Color Selector.
The buttons in this group let you determine how to generate alpha for the map. If neither map has an alpha channel, these options have no effect.
Map #1—Uses the first map's alpha channel.
Map #2—Uses the second map's alpha channel.
Multiply Alphas—Generates a new alpha channel by multiplying the alpha channels of the two maps.