One time, while flying in far north of the arctic circle, I had ALS off and there was no clouds other than haze, and the lighting was really red like that. When I turned ALS back on, the color went away. =[
I saw a sunset very much like that several years ago while I was camping on the Moelwynion in Wales. This is as it came off the camera (resized only):
Such sights are indeed very rare. It was a very still evening in late autumn, there was an inversion forming below me (which you can just make out around the hills) and the colours only got that bright for maybe 5 minutes when the angle of the sun was just right.