I have some images of the early square button stocks in my book "the AK47 catalog volume 4"..
As for the plum variant, I am not sure that existed outside prototypes. I have played with and photographed a 1991 AK74M, and it was black. And the 1990 AK/AKS74s are plum, but its so dark is almost black. 1991 stuff was black.