Don't feel bad at all. The first pink droppings I saw terrified me (until my 14-year-old pointed out that they'd been munching happily on the petals of the Impatiens). I had no idea that droppings could be colored.....
A few of my chickens ate some pink flower petals and had the same issue.....only pink instead of purple. -does sound like yours got into some berries or something of the like.