BonesOfTheMoonI don't know the reason why.
IF you’re actually curios, it was because we used to import them, and the importers would dye them red due to discoloration in how they were harvested. Domestic production ramped up in the US and since pistachios didn’t have to travel as far, and because modern harvesting was more mechanized. It was easier to wash, dry, roast and salt them in a shorter time period avoiding the discoloration that required the dye in the first place.
Captain AggravatedIt’s absolutely real; there’s a joke about it in The Naked Gun.
It’s not that there used to be a red variety of pistashio, they were sold coated in this oily red gunk that would stain your fingers pink. That stopped at some point in the late 90’s early 2000s.