While the pistachios you see today have a classic creamy light brown shell, 40 years ago, they were red. There are two main theories as to how American pistachios ended up red.
The story with the most support claims that the shells were dyed red to cover imperfections. The red dye helped make them more visually appealing for sale.
Other reports say the red dye resulted from street vendors in Brooklyn trying to stand out from the crowd. One vendor tried salting them, and another hit back by dying them.
The truth could be a mix of the stories. The end of red pistachios in the U.S. is marked by uncertainty, but they became less common when California production replaced imports.