Nope, it is just another color ELEMENT (like Red or Green or Blue) that you cant actually see.
R=255, G=255, B=255, A= 100 = Solid White - (like a wall)
R=255, G=255, B=255, A= 50 = See-through White - (like frosted glass)
R=255, G=255, B=255, A= 0 = Invisible White - (like a clear gloss-free window)

I can describe the Photoshopping of the Alpha channel, BUT FIRST make sure
that A6 actually has a function to get the alpha info. I cant find any,
all the A7 functions that can read alpha are apparently new for A7, not in A6.

If you CAN find a function that CAN read the alpha value of a models skin,
let me know and I'll write instructions of how to set up the alpha channel and
paint your body-bits in photoshop.

FOOTNOTE: Alpha is actually 0-255, but is scaled down to 0-100 by 3DGS and photoshop.