hmmm due to my version, i cant use anything related to bones.

SOB
so ill try again the alpha channel way.

if put the alpha value
eg.:
25 for arms legs
50 for body
100 for head
to be retrieve by some function that detects the alpha value of the skin..
ok
but how will i paint this values in photoshop since its RGB or CMYK?
will be something like (R=255 + G=255 + R=255) = alpha 100?