I have seen and photographed green and purple/pink aurora. The green aurora, like you describe, ranged from grey to bright green.
I only saw the purple aurora once, for about an hour, and it was quite faint but it looked like a pale pink salmon colour. I could also see the green/yellowish glow below the pink like in some of these pics, though much less intense of course:
http://hughsblog.wordpress.com/2014/...ora-australis/