Marc, I find that Jupiter gives a much better guide to a more natural colour balance, so you can port the settings you use for Jupiter over to Mars.
I prefer to capture using image settings 50:50:50 (R:G:B) and colour balance in processing, but I did experiment with getting natural colour out of the camera and it was approx. 64:50:93
FWIW your gain looks fine, those histograms look well exposed to me
