Just found this recorded session on Blender when I made the collar for the Kemono School Sweater.
The video is speeded up obviously.
[Tutorial for creators]
In the video below I show how you can make an IDMAP quickly in blender. It is very useful for the texturing process to select quickly each material (face).
And then I show how to use it in photoshop, color the part you need by using this IDMAP or create vector masks quickly !
If you are a texture artist you can fast forward to 1:34. Usually I include this map in my PSD files.