I need an adult

From what I know, it has to do with the word red covering the purple part of the spectrum long ago, and the "need" for the word purple came out later but purple things that were named red didn't get renamed.

You can look at japanese right now and 青い covers both blue and green, with a relatively recent addition of 緑 to cover only green (thus possibly pushing 青い in the future to be only blue, who knows)

Because they are only purple on the inside. Do you think apples are white? Or bananas?

in hungarian it's purple onion, you just choose the wrong language :)

why do we call green grapes white

In Spanish we actually call them "cebolla morada" that means purple onion :D

It refers to the communism of the onions

Because the dry outer skin is a rich red colour

We call them purple in Spanish... English has brain damage as per usual.

I spent way too much time sitting in the backseat looking out the window on long family drives wondering why the fuck they kept referring to the orange cheddar cheese as "yellow" cheese. Still kind of annoys me today after decades of getting older and settling down a bit.

The skin of red onions is reddish to purple. The flesh is purple much like shallots. But the skin sets them apart.

So, this is kinda weird, but general colors didn't have names for a long time. Like in Greek texts by Homer he describes the water color as dark wine color because the name "blue" wasn't a word. So it's possible when they named a "red onion" purple wasn't a color and considered a shade of red.

Also as others have said purple was the color of royalty and they didn't want an association.

Jess and Rob on Words Unraveled talk about color word origins, and their discussion is illuminating about the cultural variance in perception of color. Now I am at peace with all the seemingly weird color names for things.

For a quicker tour, Vox talks about the order that languages fill in color words as cultures begin to refine their distinction.

The inside is purple, but the outside is red, especially if it's dry.

I'm crying

What really gets me is that the compounds responsible for this hue in food are called "anthocyanins" which means "blue flower." I can't even.

I've found the color in a things name usually points to what color dye you can extract from it.

Same reason they call the tree a "Redbud tree."

Barely literate settlers were colonizing and writing home about the beautiful Puple Prule Purlple Lavendaar Red-Bud Trees.

Wait till they find out that some cultures didn't have separate words for green and blue

Calm down... calm down... Perhaps consider putting the onions aside and trying a nice parsnip.

I AM AN ADULT!

An orange is about the only thing correctly named

Nobody tell them about red cabbage

Because purple isn't a colour

It's the absence of colour your brain cannot interpret so it makes a purple.

We call em Spanish Onions round these parts

I don't know if this has anything to do with it, but it's a cool read nonetheless.

https://www.popularmechanics.com/science/a71442895/purple-is-fake-research/

Because calling them blue onions would be weird.

Purple is just an up jump red aimed at royalty

Yet purple finches clearly are red

We're not white on the Inside, so why should a red onion have to be red all the way through