Looking for Tutorial/Explanation to Create/Edit Tribes 2 Weapon Skins?

as the title says. i'm ultimately trying to create color coded versions of the default skins by editing them in gimp.

i've had to use the wayback machine to figure some of this out. i know about exogen's browser-based skinner ( Tribes 2 browser-based model viewer & skinner ) which isn't exactly what i'm looking for, although it's helped me understand hoiw the skins all need to have an alpha layer.

thing is I dont know how to gain access to the default alpha layers. is there a way to extract it out of a .png? if anybody out there has any info it would be appreciated.