Variation in eye ring color in sun conures

[Pepebirdie]

I have a random question about the variation of the eye ring in a sun conure. Why do some sun conures have dark grey/black rings while other have white rings? Here is what I mean:

vs

is it an age thing genetics or something else? Just curious.

 

[expressmailtome]

This thread discusses this topic: Skin colour change around eye? .

 

[Pixiebeak]

I will read the link. The nostril skin is also dark instead of white