Why is Onyxia purple?

[sunnycutie]

If she's a black dragon, why is she purple?

[Tommi]

Why are white people called white when they are actually pink?

[Kumorii]

Why are white people called white when they are actually pink?

I would say more biege.

[Devonitar]

She's still mostly black.

[sunnycutie]

Why are white people called white when they are actually pink?

But the black dragonflight is called black because they are black.

[Shakzor]

But the black dragonflight is called black because they are black.

She is black with purple accents, tho.
She isn't purple

[sunnycutie]

She is black with purple accents, tho.
She isn't purple

She's a lot purple.

[iscalio]

Weird question, since Onyxia is not purple, neither on art nor in the game. She has the black scales which define her dragonflight. Sure she has purple highlights, but she also has a light orange belly and white horns and yellow eyes and white teeth.
Her scales are black though. Not purple.

[Amenethor]

But the black dragonflight is called black because they are black.

The black dragons aren't actually black, they're a shade of brown.

[Nutri]

Will your next topic be "Why is Malygos grey/white"?

[1know]

She got it from her mom

[valky94]

shes black with purple accents

[kodemonkee]

What a great quality thread.

[sunnycutie]

Will your next topic be "Why is Malygos grey/white"?

He isn't.

Weird question, since Onyxia is not purple, neither on art nor in the game

She is.

[Funkyjunky]

She got it from her mom

This is pretty much accurate. Sintharia had purple features. At least before cataclysm.

[Frozenbeef]

To further differentiate her from Nefarian?

[LoLcano]

If she's a black dragon, why is she purple?

Oh, my God , you can't just ask dragons why they are purple.

[Raetary]

shes black with purple accents

Yep

[MrWolly]

Blizzard is aggressively color deficient. Take the Black War Bear for instance-the damn thing looks like it’s been rolling in blueberries!

[Aucald]

There's a few variations of colors across all the Dragonflights. While most Black dragons are the standard maroon/tan variant, both Onyxia and Sintharia's original model are black/purple, whereas Nefarian's color is more of an ashen/tan mix (darker than the standard maroon/tan). Deathwing's original coloration in art is depicted as a purple/red mix, which is the same coloration that Wrathion now has as an adult in his dragon form.