This method is for an over-all type color cast. It was a new method to me and it doesn't work on all pictures, but it can be most helpful and it's good to have in your bag of tricks!
I thought this would be a great way to start out. When I first started working with photoshop, I would create (what I thought) a beautiful picture. I would send it out to be printed and when it arrived.... WHOA.... this is not my picture!!!
So, what is going on ... watch this video by Swampy ~