Removing Global Colour Casts

Here is a really quick tip I have just discovered for removing colour casts from a image.
1. Open your image in Photoshop and press F7.
2. Copy your layer.
3. From the Filter menu select Average, this will give you the average colour of your image.
4. Change the Blend Mode of the layer to Colour.
5. From the Image menu select Adjustment/Invert, this will give you the opposite colour.
6. Simply reduce the opacity of your colour layer until you get a colour you are happy with.