document.background
This property gives access to all background attributes but it can not be used directly. It is assumed that myDoc has already been defined as a document and set as the activeDoc for the following examples.
document.background.inColor
Returns and sets the “in color” property as boolean.
myDoc.background.inColor = true
document.background.intensity
Returns and sets the intensity property as float. The property range is from 0 to 100.
myDoc.background.intensity = 50
document.background.color
Returns and sets the screen color property as RGBColor.
myDoc.background.color = "{RGB 50 80 120}"