Color bias and gradient removal are linear processes using only addition or subtraction. Color balancing uses multiplication or division. It is generally accepted that color bias correction and gradient removal should be performed before color balancing. For this exercise, the gradients were removed from the individual red, green and blue images.

This test shows that removing the color bias before or after applying color ratios makes little or no difference in the final color. However, this is no excuse for not doing the processes in the proper order. It may make a difference.

Aperture photometry subtracts the surrounding background level from a star's brightness. So addition or subtraction pixel math has little or no effect on color balance calculations. When using several stars for determining color balance, gradient removal may have a very small effect. The eXcalibrator results, in this example, were essentially identical before and after color bias removal.

Software Used:

PixInsight (PI) for gradient removal.

eXcalibrator for color balance calculations.
CCDStack for pixel math and RGB image creation.

The final image pair is the above two images with the color bias removed using pixel math. Non-linear stretching and color saturation were applied equally. These images are the answer to the original question.