-Create an M/E 1.
-Select Camera 1 in row A.
-Select DDR 1or your background image in row B.
-Select Camera 1 gear box in the bottom right corner of Camera 1 tab.
-Select Live Matte.
-Next to Color, under Matte, turn cursor to a pen, click, hold, and drag to the green screen on the preview.
-This sets the color of the green screen to the background.
To preview this, you will need to make sure the camera, lights, and the M/E 1 tab in selected or turned on.