A friend sent a nice image of M27 made using LRGB and Halpha data. The discussion below relates to how to best utilize the Halpha data in the final image
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I am not sure how you combined the data but in my experience adding Halpha to an RGB image can be tricky. It certainly can enhance the nebular detail but it can also skew the color balance, depending on how it is used
For a planetary nebula like M27, you will have line emission as the primary source of light
the strongest emission lines are Halpha, [OIII] and Hbeta. There is also [SII] and HeliumII
if you use the Halpha for luminance (not saying you did, but want to be thorough in this discussion), it will attenuate all but the Halpha and Hbeta lines.
Because fully-ionized Hydrogen will create both Halpha and Hbeta emission in a fixed ratio at the source (that ignores the differential extinction associated with propagating these two different spectral lines with their different energy levels) of about 2.92:1 in favor of the Halpha, Halpha used for luminance will tend to enhance both the Halpha and Hbeta parts of the image. Again the Hbeta will look like the Halpha in terms of shape due to that quantum mechanical emission probability I alluded to above.
Unfortunately unless the [OIII] and other lines are emitting in the same physical location (usually they have some overlap but not fully) there will be attenuation of the other species and that will both skew the color balance and if there's any reflection nebulosity, which is broadband in nature, it will attenuate it as well, causing total loss of it in some cases.
So for that reason I strongly discourage the use of Halpha for luminance.
If you combine the Halpha into the red channel data only then you will skew the ratio of the Halpha/Hbeta emission causing the colors to be skewed. The cure for that is to use the Halpha to synthesize the Hbeta and then combine the synthesized Hbeta into the Blue channel, where it falls in nature.
A reasonable first order approximation is to scale the Halpha to 30% of its intensity and sum that into the Blue filter data to create a new hybrid Blue channel. For the Red channel, you would just use the Halpha full strength mixed with the Red filter data
So the prescription I would therefore suggest is:
Red channel = Red filter data + Halpha
Green channel = Green filter data
Blue channel = Blue filter data + Hbeta =~ Blue filter data + 30%*Halpha
you can use the broadband luminance data atop this hybridized RGB and I argue that you will get a more natural color when following this prescription.
