I brewed a batch of Koelsch and used Hallertauer(3%) pellets. I have never seen such a green colored, boil foam - I wish I'd have taken a pic. The beer didn't seem to take on the color so I didn't worry about it.
When I tried to recover the yeast I noticed the green tint again on the bottom of the cake. For the second time in this batch I wondered if the hops were artificially colored (huh?)
None of my other hops have ever exhibited a color close to this but the contrast did make it easier to see the clean yeast vs. the trub / dirty yeast.
This is just as I began to swirl / flip the cake:
They don't color hop pellets, right?