Colors casts can happen for a wide variety of reasons ranging from white balance issues to weird venue lighting or poor filter design. And just like the multitude of reasons for their presence, there are numerous ways to fix them. This technique allows you to quickly and precisely zero in on the corrective color you need without needing to eyeball it, making it one you'll definitely want to know.
Coming to you from Blake Rudis of f.64 Academy, this helpful tutorial will show you a clever method for correcting color casts and subsequently grading an image. Color casts are one of those annoying things that you can spend a long time staring at, nudging sliders back and forth to get the right result. This trick bypasses the need to eyeball the image, instead relying on the neat trick of inverting the image, using the Average blur filter (this calculates the average color of a layer, then fills the layer with it), and then applying it to the original image using the Soft Light blending mode. This works because a color cast is generally a global property of an image, and you're trying to find the complement of that global color to offset it. It's a neat and rather effective trick. Try it out!