Maybe I'm being obtuse, but I didn't glean from the link why folks simply didn't opt for no pigment (which I assume results in some sort of unappealing gray or brown). Do you know why?
Because the pigment is what protects what's under paint from UV light. With no pigment you have in effect varnish. Also, without some kind of pigment you might have to use excessive amounts of binder to get a sufficiently thick coat.
Ahh... I was ignorant; I assumed the pigment provided only color. Thanks.