I stumbled upon this rather neat effect while tinkering with 2/0 nodes with Apollo. I don't yet fully understand why changing this one value does this but I'm investigating. It appears that it has something to do with the alpha component in the TGA. I'd say this Turm has seen some better days. Looks like someone forgot to replace the sacrificial anodes during PMs...
edit: extracted out the TGAs and none of them have alpha channels so it's not the alpha component causing this. Hmmm.....