the AAO image looks noisy and the color shades depend on the noise, too. don't they. that's where the yellow tint (the brown) comes from.
the 2 images that have a clear black (as in 'no noise') as background
http://www.cosmotography.com/images/small_m17.html
and
http://www.astro-pics.com/17plm.htm
are less brown and overall show more differences in the nebula color.
myself being far from producing such images, I still have my own taste - and that goes for more nuances.
the pink in your image, michael, is stunning and like candy floss.
a looker.
but not my cup of tea.
