How make plot PNG have transparent background? (i.e. same background color as web page?)

Matplotlib PNGs by default has a nice white background.

    > What if you want to put the PNGs in a blue web page?

    > Is there a way to make PNGs inherit background colors of
    > web pages?

You can set the alpha property of any matplotlib figure element. The
two entities of interest here are the figure patch (rectangle
background) and axes patch (ditto)

  #0 is transparent, 1 is opaque