I don't know gimp, but in PhotoShop there are several ways to temper it. I'll tell you what I would do and maybe you know the equivalent in gimp.
First I would try the curves function which allows you to set a black, white or middle gray point using the eye dropper tool. Using the eye dropper, you select an area of the photograph that should be true white or true middle gray. I usually prefer the middle gray result, but sometimes the white point is better. Very often this is all you need to do.
Another option is to use a selective color adjustment. In PS, there is a dialog box that allows you to select the color you want to modify (white, red, bye, green, etc). I would select white, then adjust the cyan slider until white looks white. There are other sliders, so I would adjust until it looks right.
If either of these didn't work, my last resort would be to use a red color overlay at some reduced opacity (25%?) to counteract the green.
I hope this will at least give you an idea of what you can try. Good luck!
I once saw engagement photos done by a well known and very expensive So Cal photographer in which about 75 of the proofs were shot with tungsten white balance and the photos were all outdoors. Everything was a lovely shade of blue!
