Okay, this picture

is completely awesome, BUT

But they should have more of the SIN colour on the bottom of wings, right? Because touching the bottom of a bird's wing is a courtship gesture, I think that the whole inside of the wings should be at least slightly more sensitive than the outside.

So then it would make sense that the 'don't touch it or I won't control myself' usually applies to under the wings. It's like, a giant tease more intense than anything. It's like, at the point where you both have your shirts off the other just walks away with a wink and a smirk. It's like, not very nice for the angel, and that's why they ask that the person touching their wings don't stop, because it's then, when there's no more contact in their wings, that they'll crave for more and use the cliché 'I pin you to the wall' thing.

I also think that the outside of the wings would have a lustful reaction, whereas the inside would have a pleasured reaction, or maybe it's the other way around, I don't know, figure it out by yourself now.

I also have this headcanon that if not sensitive in the 'sex' sense of it, wings would be extra ticklish. Like, imagina a human Luci passing a hand in Mickey's wings and it makes him burst out in laughter.