Like this example... Can't remember if this is one that I made or somebody elses but it's easy enough to do in an image editor, use SnowSultan's seam guide for the appropriate figure as a template. Her guides have colored delineations for the texture or material regions of the mesh... looking at this one it could perhaps have a wee bit more blur, didn't test it.

http://www.snowsultan.com/3.html

Edit- Think this particular mask might be FleshForge's on ShareCG.

http://www.sharecg.com/v/46983/gallery/11/Poser/V4-Lip-Mask-Bitmap