on reviewing Kairos again the black section just looks unfinished. I think there are 3 ways got could go with his wings without repainting the whole model.
1) leave the black edge as it is with the green and blend down to the wing tips using a fiery red/orange
2) paint a star field on the black of wings, as though the void of space is encompassed there
3) back to my favorite idea, make the black a multicolored iridescent oil slick of changing colors
There's even a paint that does it.
Schmincke "Aero vision space"
In going to try and get my hands on this stuff too, even at $30 bottle.