Advanced Color Correcting Using the 3-Way Color Corrector in FCP

Step 4: Overlay Top Layer

As you can now see in your Canvas window, your clip hasn't changed yet. The only visible change is the tinted, bottom layer which you can see in the Viewer window. In the next step the fun begins and you'll start seeing your clip transform.

Right click on the top layer go down to Composite Mode then select Overlay.