Add a transition between color corrections
You can have a video clip change from one color correction to another using a transition. For example, if you want a scene to gradually highlight the face of an actor, you can use a transition to dissolve between the normal clip and a second instance of the clip with a shape mask around the face and a color correction applied that darkens the image outside of the mask.
Add a transition between two color corrections
Temporarily switch to the Blade tool by holding down the B key.
In the Timeline, click a video clip at the point where you want to change between color corrections.
The clip splits into two clips.
Apply a different color correction to each clip.
Select the edit point between the two clips, and press Command-T to insert a cross dissolve.
When you play the clip, one color correction dissolves into the other as the edit point is passed.