An image can have a global color cast for a wide variety of reasons, and there are a multitude of techniques for correcting such issues. This clever technique can resolve a color cast with one click and also provides a way to do so for more difficult images.
Coming to you from Unmesh Dinda of PiXimperfect, this helpful video shows you how to use Curves adjustment layers to correct the color in an image. The technique is rather simple: you use the gray eyedropper tool to select an area of your image that should be gray. Once you've done that, Photoshop automatically adjusts the image so that point actually is gray. As an additional tip, I recommend changing from point sampling to something like 3x3 average to make sure you don't get an odd result if you click one anomalous pixel. Dinda goes on to show a clever workaround for instances where you don't have an obvious patch of gray, which takes advantage of the difference blending mode to show which areas have the smallest gap between themselves and gray, or in other words, are closest to gray and thus what you should use for the eyedropper correction trick. It's a quick and effective technique!