The old (but still present) non-channel based method calculated brightness differences based on the median of green channel (because that's that most reliable channel) and (if enabled) applied the correction factor to red, green and blue channel (think about it as a simple brightness detection in green channel)
The new (optional) method calculates brightness differences for each channel based on the median of each channel.
For the example I posted on github the factors are:
blue brightness factors by median : 1.14893 1.09496 1.03999 1
red brightness factors by median : 1.12032 1.07768 1.03366 1
green brightness factors by median : 1.14102 1.08832 1.03719 1
In left view of second screenshot on github green brightness factor was used for all channels while in right view for each channel the per channel (red/green/blue) brightness factor were used,