This is a really easy quick way to correct the colour of an image / photo. First off below is an image of my friend that I took (to turn it into a Star Wars thing with a lightsaber etc) but as you can see it's gota horrible green / yellow thing going on and I want to get rid of it. Start off by duplicating the background layer. Now select Filter > Blur > Average. This will give you the average colour of all the pixels of the image. Now this is the colour that we would like to get rid of and to do that we'll need to apply the opposite colour to the image. Hold CRTL and press I to invert the colour. Now select "Colour" from the layer blending mode drop down box. As you can see from the image below this will give it the tint of the opposite colour we want to get rid of, however some adjusting is still required. Adjust the opacity until you have a nice colour balance and there you go, your image should be a massive improvement on what you started off with. Hope it helps you out!