Result of me being tired of the wing-colour argument. Also, reference to the Cthulhu Mythos' Hastur, "The King in Yellow", because I'll never get tired of that joke.
Demon wings are the same as angel wings. But no two sets of wings on either side are exactly the same.
Beelzebub and Metatron bore flames instead of feathers, red and gold.
Azrael's were wing-shaped holes in space, star-sprinkled.
Hastur, since the incident at Arkham, had become famous among demonologists for his wings; brimstone yellow. Ligur's were shadowy grey. Vague memories of gold and silver wings occasionally nagged at Crowley.
As he sat beside Aziraphale, the angel's white wings brushed against Crowley's black. One like pearl, the other like an oil slick. Both shone with rainbows, in the right light.