I received a criticism that there were too excessive blue/purple halos around the stars in my M27 image.
It has taken me ages to come up with a solution but here it is.
Starting with my previously processed image:
(i) Load image into Photoshop CS6.
(ii) Duplicate layer.
(iii) Add mask to duplicate layer. Use brush (137 pixel, airbrush soft round 50% flow) to cover nebula in mask on duplicate layer.
(iv) De-select bottom layer (without mask) so not visible.
(v) Go to duplicate layer (not mask) and open levels and raise lower limit on blue level until blue halo disappears.
(vi) Re-select bottom layer so visible again.
Voila! Blues gone but nebula still original colour!