Hi, I also experienced white aurora with my own eyes. It was in the night from 19./20. of December in 2015. There were two incoming CMEs right behind and auroral activity was very high. I was sitting near Tromsö with my camera and was waiting. Unfortunately, whole scandinavia was coverd in clouds on that night
I waited the whole night, until around 5:00 UTC in the morning. Then, a hole was formed in the clouds.
I saw those white rays and I was able to take some pictures. The hole in the clouds was exactly above my head.
I also do not understand on which factors the aurora appearance is dependent. I have typical pictures attached. Sometimes there is an aurora with very long rays and many colors ( I think this is the "picket fence") and sometimes the (at least for me) "more normal" shape where the aurora band is much more narrow andon the down side you have the typical color bands of white and magenta (last picture).
I don't think that it is just the overall activity. The pictures of the colorful auroras where taken in the same night and activity was average (like Kp 4).