What the hell happened to her puss? Is that necrosis? This would actually be a fine piece, but damn this artist chose a really bad color for vagina.

That's just natural for some people? The amount of melanin varies a lot from person to person, see also dark nipples.

Shinjidude said in comment #2596399:

That's just natural for some people? The amount of melanin varies a lot from person to person, see also dark nipples.

Even considering melanin expression difference that's still too dark, not to mention the place where hyperpigmentation occurs was wrong. Normally the lips gets darker color and graduate to lighter the closer to vaginal canal, but in this case it's reversed.

And since you brought out the melanin expression, the 'carpet matches the drapes' rule applies here: the color of nips are closely related with the color of your labia, along with the color of your lips. You can't have such extreme degree of difference from pink tips but black underlips unless something like medical manipulation (nipple color changing procedure like lasering) was done.

Edit: you know what, it looks like abalone. Surely the artist didn't take that 'pussies looks like abalone' thing and made this piece because the other pictures has correct anatomy?