Hmm. I know vertex color is stored by default in UV channel 0. But where are illum and alpha stored? I don't think they can be in the same channel because there are only three numbers per vertex.. U V and W, which I guess correspond to RGB. Do you know where they're stored? In 5.1 I've been using a v4 modifier plugin…
Been playing around with the new Substance Designer nodes, and trying to figure out ways to layer pebbles\stones without obvious intersections. https://www.artstation.com/artwork/19ZW3 https://gumroad.com/l/whWrk
Heres a tut I made a whole ago. It's based on creating a stone texture, but the general idea is still there. Hope it helps. http://www.smileybones.com/?page_id=316