That purple Sister is genuine - SST pressed them (along with pink EVOLs) around 1990. Not worth $750, but usually makes 3-figures.
So far, the only coloured boots to show up are Goo (claiming to be a German pressing, as detailed at the start of this thread) and the new "Blast First" EVOLs.
And as I said in the other thread, there's been coloured boots of popular LPs by loads of "major" bands over the last couple of years - you can see other examples sold by the same eBay sellers that have these SY ones. They're all using new plates rather than using original stampers, as evidenced the the matrix being just a hand scratched catalog number rather than the "proper" ones.