I find the current handling of background colors very non-intuitive:

1. figure facecolor is not applied for savefig() by default
2. figure facecolor is not applied setting frameon=False
3. axis_bgcolor is not applied when hiding axis lines/ticks via axis('off')

So using a white plain surface to draw objects needs the following code:

fig = figure(..., facecolor='w', edgecolor='None')
ax.axis('equal')        # equal scale
ax.axis('off')          # do not show axis
ax.axis([-1, 1, -1, 1]) # scale to unit lengths
show()
fig.savefig(..., facecolor=fig.get_facecolor(), edgecolor='None', transparent=True)

My suggestion

• apply same colors to savefig() by default
• mention in the docs of axis_bgcolor and axis('off') that this setting is ignored
• mention in the docs of facecolor and frameon that this setting is ignored