Pie chart is "stretched"

Hi all,

I'm trying to generate a pie chart to use in my django web app. But
it keeps rendering in a rectanuglar canvas instead of a square one, so
the pie is oblong instead of circular. It also keeps rendering with a
grey background, I need the background to be white.

I've attached a jpg of the chart - here is my source.

def chart(request):
    from PIL import Image as PILImage
    from matplotlib.backends.backend_agg import FigureCanvasAgg as FigureCanvas
    from matplotlib.figure import Figure
    from StringIO import StringIO
    fig = Figure()
    canvas = FigureCanvas(fig)
    ax = fig.add_subplot(111)
    labels = 'Frogs', 'Hogs', 'Dogs', 'Logs'
    fracs = [15,30,45, 10]
    ax.pie(fracs, labels=labels, shadow=True)
    #ax.set_title('hi mom')
    size = canvas.get_renderer().get_canvas_width_height()
    im=PILImage.fromstring('RGB', size, buf, 'raw', 'RGB', 0, 1)
    im.save(imdata, format='JPEG')
    response = HttpResponse(imdata.getvalue(), mimetype='image/jpeg')
    return response

Also - can I choose my own colors for the slices?