A bit more detail:
A new argument ?backgroundColor is added to command saveGraphImage to allow
saving graph image with a user specified color.
Default value : Current background color of graph image (nil).
To save a graph image with 'light grey' background color.
saveGraphImage(?window window ?fileName "check.jpg" ?backgroundColor "light grey")
To save with current background color of graph(default behavior)
saveGraphImage(?window window ?fileName "check.jpg" ?backgroundColor nil)
This is in IC616. Just means that you've got the option to change the background colour at the same time as saving an image.