Comment 2 for bug 339754

I don't think the default should be fully transparent as it's less needed than the white-to-gray.
That said, on revision 30 the white-to-gray background is still the default, but it's now possible to pass color strings for the background. Whenever you wish a transparent background, just pass it like this:

data = [1,2,3,4,5,6,7,8,9,10,11,12,13,14]
cairoplot.vertical_bar_plot ( 'bar_background_color', data, 400, 300, background = "transparent", border = 20, grid = True)