The magenta in the Ha areas comes from the unfortunate side effect of heavy colour balance adjustment of raw files due to heavy red/pink colour cast. A part of my workflow I will need to investigate.
Seems to be some debate on what the real colour of Ha looks like. Using a clip in Ha filter in my full spectrum 6D, the response from the red pixels is overwhelmingly dominant, but there is some blue pixel response, so the end result is a deep red/burgundy rather than a magenta. or bold red. The blue response increases the deeper you go into infrared.
As far as how 656nm looks to the human eye, my 650nm IR and clip in 12nm Ha filters look deep red/burgundy to my eyes.
Here is a retouched version of the original that I posted with some colour adjustments.
I don't know (or care) much about AP, but for some reason I'm finding this image spectacularly good. It has that 3D feel about it that most (but not all) others lack. This isn't just a picture of some DSO, this is a picture of Space.
