From Evernote:

Figure Settings Matplotlib

In Lion, all figure settings live inside

/Library/Python/2.7/site-packages/matplotlib/mpl-data/matplotlibrc

You can modify such file, however it will be overwritten on the next python update. 

Instead to have your user-defined changes in a save place, write your changes to this location

/Users/myuser/.matplotlib/matplotlibrc