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 Background Image zone and one video zone (or more with Mosaic mode), while single-video models (e.g. HDx23, LS423) do not support both a video zone and Background Image zone simultaneously.
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.