This window controls the operation of overlay objects such as the opacity of
the overlay and fading. You can either turn the overlay off, or define an RGB
key which controls the transparent color. Objects behind the overly are visible
where the color in the overlay matches the RGB key.
Opacity defines how much of the background is visible through the overlay for
non-transparent colors. Fade In fades to the defined opacity at the beginning of the object and Fade Out does so at the end. The Fade Time setting controls the duration of the fading.