FULL TUTORIAL: http://photography.tutsplus.com/tutorials/how-to-use-blend-if-in-adobe-photoshop-in-60-seconds--cms-25782?utm_campaign=yt_tutsplus_cr3p-5xV1Hg&utm_medium=referral&utm_source=youtube.com&utm_content=description

The Blend If sliders are one of Adobe Photoshop's most powerful layer blending options. They give you an incredibly nuanced control over how information from two separate layers is combined based on their luminosity values.

In the screencast above, I show the Blend If sliders in action. I want to give this photo a Hollywood style teal-orange tone. I use two solid colour layers set to the colour blend mode—one called shadows which is teal and the other called highlights which is orange—to tone the image.