At the sight of blackbirds Flying in a green light, Even the bawds of euphony Would cry out sharply.
This passage sounds beautiful, but its meaning is so unclear! That's poetry for you. But we can help.
The speaker says that even people who enjoy cheap pleasures can feel intense emotion at the sight of "blackbirds flying in a green light."
A "bawd" is a female pimp, someone who arranges for someone else to buy pleasure. And "euphony" is a nice, pleasing sound, but Stevens uses it ironically to mean a saccharine or schmaltzy sound (source). So, a "bawd of euphony" is a very obscure name for someone who reduces a complex beauty to a cheap pleasure. If it helps, the opposite of euphony is "cacophony," or random noise.
The blackbird in the green light is a complex pleasure. We don't know why the light is green, but maybe the bird is flying underneath a sunny, green tree. The contrast between green light and a black bird does not produce a soothing euphony. So, in theory, the bawds of euphony should be like, "Nope, not interested."
But instead, those pesky bawds "cry out sharply" as if from pleasure, pain, or both. They don't know how to process this amazing new sight.