A Blender add-on to create vertex color layers that can be used as an ID-map

If you have a mesh with lots of materials you can create a set of textures for each material but with lots of textures you will quickly hit the the limitations of your GPU memory. Also a lot of space in each texture will probably not be  used efficiently.

Texture painting programs like Substance Painter can of course create one texture set for the whole mesh but then you need an easy way to select which parts of a mesh should get which type of material. Providing an ID-map in the form of a vertex color layer is the simplest way to achieve this. Substance Painter will use this by default when baking textures and offers the option to add a color selection mask to each material where you can pick one or more colors from your ID-map with an eye-dropper.

No, any program that can utilize a vertex color layer for this purpose will probably work, but I tested it with Substance Painter.

Blender's vertex paint mode applies colors to vertices, not to faces. This is very useful if you want to use vertex colors artistically, for example as input for a shader where blending colors over a face is an advantage but ID-maps mostly expect each face to have a uniform color so we need a way to paint and manipulate regions of color on a face-by-face basis. IDMapper's Face Paint mode provides exactly that.

IDMapper offers a panel in the Toolbar where yo can load a .csv file that contains color definitions. In Face Paint mode you can select a color from this list and apply to all regions of a given color with Alt-K. By using this list for different meshes you can quickly replace the randomly assigned colors by colors from this list.

IDMapper offers a panel in the Toolbar where yo can load a .csv file that contains color definitions. In Face Paint mode you can select a color from this list and apply to all regions of a given color with Alt-K. By using this list for different meshes you can quickly replace the randomly assigned colors by colors from this list.