I have twice noticed that when I microwave an artichoke in a bowl with a 1/2
inch of water in the bottom of it, that the liquid that remains is later a
pretty shade of green. Last night I did this, and specifically noticed that
the liquid was not green at the bottom of the bowl when I was done cooking
and had removed the artichoke to eat, but this morning saw that this water
had turned green.

What is happening here?

Reece