They're sometimes called candy cane beets. I used to work on a farm and we grew all kinds of cool colored and patterned beets.

The German term is "Ringelbete" it's a variant that's supposed to taste a bit more mild and less earthy. Afaik it's mostly used because it looks pretty or if people are not into the usual beet flavor.

It's a Chioggia beet, mostly for cool decoration on a plate.

This is the beet they were talking about when they were singing "Give me the beet now and free my soul"

Im a huge fane of Psychedelic Beets

Onion-beet!

Beets me!

I've cooked ones like this before, but they never tasted as good as the fully red ones. I guess it's probably due to insufficient water so the beet's not juicy.