The Background Image zone allows you to place an image or media feed in the background of your presentation. All other zones appear on top of this zone. You cannot edit the Zone Properties for a Background Image zone.
The Background Image zone consumes a video decoder on the BrightSign player. If the player model supports two video zones (e.g. XTx43, XDx33), it can support one video zone and one Background Image zone, while single-video models (e.g. HDx23, LS423) do not support both a video zone and Background Image zone simultaneously. Note that on some models this rule does not apply to Mosaic mode presentations.
If you only want a background color (instead of an image), do not add a Background Image zone. Instead, change the background screen color in the File > Presentation Properties > Main tab.