green light is notifications. blue light could be "do not disturb" is enable.
I have not gotten a green light yet, but the light blue (almost white) is in fact for alerts & notifications.I know this because I get them regularly. I then ask "Alexa, what are my alerts (or notifications)" and Alexa tells me.
If I turn "do not disturb" on my devices, I see a quick purple ring & then nothing. The light does not stay on.
Are you using different devices than I am?
I have an Echo Show, an Echo Spot, one 2nd gen Dot, three 3rd Gen Dots, and a Fire tablet, all of which, if capable, exhibit this behavior.