I'll press ahead ... let me show you one of my favourite methods: Download PSD file
It will perhaps look more complicated than it truly is. Basically, you choose a colour which is most desirable for the background (that is, most similar to the existing background, or an average thereof) and add a Solid Color layer of that colour. Then immediately invert the mask of that layer to black, then duplicate the layer three times. So you will have four identical Solid Color layers, all of them hidden by their black masks.
Then:
change the blend mode of the first layer to "Multiply". That will be the layer that you use to gently darken the too-light areas
change the blend mode of the second layer to "Screen". That one will be for lightening too-dark areas
change the blend mode of the third layer to "Color". That will be the layer you use to fix any wrong-coloured areas
leave the blend mode of the fourth layer on "Normal". That will be your actual backdrop layer.
Then paint on the mask of the top layer everywhere, and close to the hair, but don't quite touch the hair.
Then use a very low opacity brush to "massage" the other three layers as needed, until everything blends nicely.
(I've also added one more layer at the top of the file, to demonstrate changing the colour of the finished background.)