I'm beginning to do galaxy work on an ASI 183mm Pro with Astronomik deep sky filters. I'm getting stars that are multiple colors. I posted an image link to what I am talking about. Maybe it's my tracking or maybe it's from stars being bigger in one filter than another. They are taken by guiding on an AVX mount and sometimes on the guiding the RMS error is only 0.68 arcsec/pix. That seems pretty good for my mount. The telescope I'm using is the Skywatcher 72ED, which seems to be good with this camera. I'm using a field flattner from Orion, but it's not a reducer. Plate solved images show a 1.15"/pix image scale and the focal length is 430mm.
The image is the area around M101, the galaxy is also there. I use Pixinsight to process my images. I'm wanting to ask if I bin 2x2 for the RGB subs and do bin 1x1 for luminance, if the stars may be more uniform between RGB stacks? I'm open to try other things, but right now I don't know what to do. I also image in narrowband and it's not as noticeable there. During preprocessing in the star alignment process, I use the same sub for all RGB channels to be aligned as a reference image.