With the success of PCC, using the ASG white reference, I don't see the need for using any of the other PixInsight color calibration procedures. However, if you want to show a reddened galaxy with its intrinsic color, you can still do so. But remember, you will have incorrect color in the foreground stars.

Here is how PixInsight PCC compares with eXcalibrator.

eXcalibrator has two photometric calibration routines. The eXcalibrator Classic (white star) method uses stars, of any type, that should appear white. With galactic extinction, some slightly blue stars can appear white. Secondly, eXcalibrator has a linear regression routine. This uses stars that should appear slightly blue to white and to yellow. These two methods usually get similar and often identical results.

I processed 25 images that included galaxies, emission nebulae, clusters and reflection nebulae. The results were normalized to the red. PCC consistently had slightly bluer/cyan results. The two programs always agreed in the general direction of the color correction.

PCC (Average Spiral Galaxy) vs eXcal (Linerar Regression)
PCC averaged 6.12% more blue
Std Dev 5.57
90% confidence 4.29% to 7.95%

PCC averaged 1.28% more green
Std Dev 3.13
90% confidence 0.25% to 2.31%

PCC (G2V) vs eXcal (White Star)
eXcal averaged 12.67% more blue
Std Dev 3.31
90% confidence 11.26% to 14.07%

eXcal averaged 7.27% more green
Std Dev 3.13
90% confidence 5.94% to 8.60%
 

With galaxies and clusters the difference in the two programs was less than the average, with PCC consistently bluer. With images, dominated by nebula, the difference was greater than the average, with PCC still bluer. This may indicate a difference in eXcalibrator's use of Source Extractor aperture photometry and PixInsight's implementation. At the high-end of the 90% confidence range, emission nebula will very likely look a bit bluer with the PCC results.

A 4 to 8% change in color can be difficult to detect, especially with LRGB images. For some, it may require blinking the images. Others, with slightly diminished color vision, will not see the difference.

The following two images share the same luminance. With the eXcalibrator image, the blue was reduced by 6.12% and the green by 1.28%. The images were processed identically with PixInsight.  The PCC image is noticeably bluer in the spiral arms and eXcalibrator has stronger red in the core.

Without the luminance data, the images show a slightly stronger difference. The PCC image has more faint detail in the blue arms. However, with galaxies, this is probably meaningless as most users create LRGB images.

Can you see the difference? :-)