Green flowers seem unusual, but maybe they are not, precisely because they are not noticed very easily. But your point about insects not seeing them is a good one; we had a cactus in the house that finally set bloom after many years... and it was bright green. Quite a surprise.
=^..^=
I've never seen a green cactus flower, what kind is it?
I believe it is called a "Teddy Bear Cholla." My Humans were told it was "impossible" to grow it as a houseplant, let alone to get it to flower. Then this happened:
=^..^=
That does look like something that wants to grow outside in full sun. Impressive!