[kaybe]

It's definitely green (and a little blue and red if you're lucky). You'd have to be massively colourblind to not see this. The ground though.. just like with the moon, it's still greyish, that part is usually from long exposure (so the photographs with a bright ground are suspicious indeed, same for blurred (or line!) stars).

The strong lights can be moving quite fast, so they're more blurred even in pictures with low acquisition times.

But again, it's hear-say as you say. Here is a more official scale for brightness:

https://cloudatlas.wmo.int/polar-aurora-brightness.html

edit: Actually, the first picture in the article looks pretty realistic!