Digital Light & Color

This is a silly question because I feel I should know how to answer it by now, but I don't seem to be doing well.

There are two pictures (portraits) on the same blue background. For whatever reason (I haven't taken them), be it the light colour or more likely postprocessing, their tint is visibly different - both faces and the background. I'm trying to make the one look like the other.

One idea was that if I filter it somehow so that the blue background match, I could equalize their global tint and the process them both the same way from this point on. I tried Colour Balance - Remove one background and Add the other - but the results are not great. There must be a simpler way, I just can't think of it...

Color Balance by white balancing the whites of the eyes usually works well for portraits. If the light changed, it may not be possible to match both the backgrounds and the figures.