When in a room, it can have no background image selected for any
of its background_index, in which
case you should set a background colour with the background_colour variable
and make sure that it is visible by setting this variable is set to
true. Having a room with no background image and no
background colour will result in graphical artefacts being drawn on
the screen and is not recommended.
if background_index == -1
background_colour = c_black;
background_showcolour = true;
The above code checks to see if background0 has an image assigned to it and if not it sets the background colour to black and flags it to be shown.