This is not a scientific survey, but I whipped out my 1970 album and looked at the backs of all the pages and, sure enough, an occasional card with a blatantly white back showed up now and again. They were prominently in the lower numbers and then disappeared altogether until the 500-600's when a couple more of them reappeared.
In my set, at least, everything was cream colored except these aberrational white backs. For you specifically, Joe, I noticed a white back #5, Wes Parker, but now I hate you, because this exercise did nothing except make me realize how many more cards I need to upgrade in this set. Ugh!!
