That White Dog Poop from the '70s

An episode of the Sarah Silverman program showed Sarah asking "whatever happened to that white dog poop from the '70s?" I was all like "yeah!?" Nick reminded me that I wasn't alive during the '70s. I agreed, but remembered that I had seen white dog poop in my earlier years. What's different these days that crap doesn't change colors like that? I think it's something different in the food. Otherwise, I can't explain it. I don't think that dog physiology or ambient conditions have changed enough to make all dog poop stop turning white. What kind of regulations were passed to keep whiteners out of dog food? Is it because all the whitening agents are now being diverted to toothpaste manufacturers?