I also thought there was only one Proofide, and I'm not going to dig up mine to confirm the spelling. You should keep in mind that Amazon pretty much accepts product descriptions as presented by their various vendors. You should probably go to the Brooks website for confirmation.
I'm pretty sure stains from the saddle have more to do with the dye, though some of it might dissolve in the proofhide and transfer to the shorts. I wouldn't wear white shorts with a black Brooks, regardless of leather treatment.
I use saddle soap for cleaning leather shoes. Put it on thick, and wipe (not rinse) it off. I suppose I would use it on a saddle if I ever wanted to wash it. The stuff is supposed to replace oil in the leather when washing, but I would not use it as a leather conditioner.
There you have it, James. No answer at all.
Some people are like a Slinky ... not really good for anything, but you still can't help but smile when you shove them down the stairs.