I cant find pics, but copper pesticides are a deep blue color (because of the oxidation state of the copper). At least thats how it looks when you mix it before applying. You never use enough to actually color the body of water, and you’re right it probably turns more greenish after being applied.

fill it with some industrial petroleum dye that’ll mutate the ducks

Methylene blue lets gooooo! Put me in the situation room ill find a solution to this