Museum of Time
painting the sky
The light from aurora is strictly monochrome: red and green from oxygen (630 and 557 nm) and blue from nitrogen (427 nm).

During large geomagnetic storms you can usually see multiple auroral curtains behind each other and the colors then mix.
In this filmclip of 11 April 2001 you can see the sky change from a shouting neon-like red/green to pastel crayons.

watch 25 sec
Quicktime filmclip