public RGBA get_color_background_for_draw ()
Returns the background colour, as used by this when drawing the background, which may be different from the color set by set_color_background.
Note: you must only call this function while handling the GtkWidget::draw signal.
This function is rarely useful. One use for it is if you disable drawing the background (see set_clear_background) and then need to draw the background yourself.
a location to store a RGBA color