color_cluster.lua files are used by the game to see which parts of the model are customizable.
.lua files can be opened with Microsoft Word. You'll find something like this:
The file is divided in clusters. Each cluster is a slot in the color selection menu. The maximum number of slots you can use is 10. A bigger number makes the game crash. Each one has this information:
A name for the cluster [Green]: Just a name for the modder, it doesn't affect the game.
Type [Red]: The name that appears in the color selection menu. SKIN, HAIR, CLOTH or PART. Can be followed by a number.
Neon colors [Blue]: True = Enabled, False = Disabled
Metal colors effect [Purple]: True = Enabled, False = Disabled
Main part of the cluster [Yellow]: Use one of the parts of the cluster. This line is used to show the selected and possible colors.
A=Selected color. B=Possible colors. The material name you write tells the game which colors must place there (from the obj.emm files).
Parts of the cluster [Cyan]: The most important info. It contains the name of the parts (materials) which will all use the same color. The number in the right explains which layer of the texture file will use each part. 0 = Red layer, 1 = Green layer, 2 = Blue layer If followed by "dominant=true", it will use only that layer's info if the texture layers overlap (used by most of the parts). Not needed if the number is 0. This can be used to paint with different colors some parts of the same object. In the example, the 'face_hada' material has two different colors. The one of the 'SKIN' cluster will use the red layer textures and the one of the 'HAIR' cluster will use the green layer textures. The color used is the one specified in the obj.emm files.
I hope this info is useful.