Select this checkbox if you want to apply the effect
Select this radio button to apply an image as background (It can be a custom image from your PC or a preset image)
Select this radio button to apply a solid color as background
Select this radio button to apply a video as background. The video background is composed of 60 frames equally spaced throughout the duration of the video (e.g. Video Background is 60sec. This means every video background frame is 1 sec apart)
Your background doesn't necessarily need to be colored green to have this effect working. This button lets you select the color of your background. You may use the button to select the color from the gradient box or the eye dropper button to specifically click on the monitor what pixel color to replace.
This slider lets you have the flexibility to extend the range of the color you are replacing.