Tutorials for Gimp

After the color correction

Before the color correction

Step 1: What color needs to be corrected.

Activate the Color Pick Tool and click in an area of the image that should be (but isn't) white, for example the white of the eyes.
If there aren't any white areas in the image take the most neutral (gray) area of the image.
By doing this you've determent the color that need to be corrected and have set it as the foreground color.

Click on the foreground color and set the Saturation (S) to 100 and the Value (V) to 60.

Step 2: The color correction.

Create a new layer and fill it with the foreground color.
While the new colored layer is active go to Color > Invert.
Change the blend mode of this layer to Overlay.

In most cases the result is not good yet. You'll get an other colorcast.
All you have to do now is to lower the opacity of this layer. The value depends of the image you're working on.