In the US, "ginger" is a seasoning, not a color. Like, in general; we do not refer to anything as being ginger-colored unless it's a sort of pale yellowish tan.

The redhead, ginger, color link comes from early season ginger, which has reddish pink tips around the leaves right above the fresh root.

People will still refer to redheads as "ginger" but only some of the time

That's a fairly new thing. Growing up, I never heard anyone use "ginger" in that way. It was always "redhead." Or sometimes "strawberry blonde" for lighter shades.

Millennial checking in, ginger was used all the time when I was a kid

Only a ginger should call another person ginger.

https://www.youtube.com/watch?v=KVN_0qvuhhw

In UK English ginger isn't exactly a color either. It's not like yellow or orange. It's a state of being.

I don't know why this is being downvoted. Does "ginger-colored" sound right to you? It doesn't quite work.

It's true. A person is ginger, but nobody ever says things are ginger coloured. Ginger isn't even really one colour - it's a spectrum of orange-containing hair colours.

If you would then please explain the "kick a ginger day" from SouthPark

South Park popularized it. It was known but not common before that where I lived. It also popularized harassing them in general at my school.

Were there many reds around when you were growing up? My family is full of redheads, and ginger was a well known term to me. I'm much older than South Park

No, only a couple that I knew of. My area was mostly Mexican, then white, then native, then everything else.

Old south-park is no longer culturally relevant.