Here's a repro of NGC 6188, I'm happier with on more natural colours, and what a range there is in this nebula.
This was done with a tip I recieved for Photoshop.
When working in curves, set the white point on a white star and the black part on a known black part of the image like the dusty nebula. All the data is in these two point and it also help from any clipping that might happen. When it starts to get grainy, that's the limit of your data so I don't try to force data. You can either get more subs or add more temp matched darks to extract a bit more details.
