It's kinda hard to say - I mean, I've never thought about it before.
Because I'm sexually attracted to women, that might have a bearing on my perception that her vagina is beautiful or gorgeous or whatever. As many people have stated so far, there are many factors that come into play when saying something is beautiful. Because "beauty" is different from person to person, it isn't easy to pinpoint exactly what constitutes a beautiful pussy. There are probably some standards, like lip size, amount of hair, amount of fat on the mons, whether the lips are open or closed, amount of natural lubrication, etc. The list could go on.
For me, it's not complicated at all. There are very few women that had a vagina I didn't think had some level of beauty to it. For the those that I felt negatively about, it surrounded the total package of the woman that turned me off from them - not just the vagina. So the things I find unattractive in a woman will turn me off from her completely - and therefore her vagina may not be as attractive either. I like a woman's vagina, so when I see one it instantly turns me on - because I want to taste, lick, and be inside it.
It's probably instinctual - the reasons why I think a woman's vagina is beautiful. Those are just my thoughts on the subject. Thanks for listening.
Simba