Region Adjacency Graph

## Example Images
![figure_1](https://cloud.githubusercontent.com/assets/3823490/3291718/5ce9b952-f587-11e3-8c29-e2aace6d7794.png)
![figure_2](https://cloud.githubusercontent.com/assets/3823490/3291723/7074b134-f587-11e3-8c73-d28222891a21.png)


This is a weird line break... I would do:
```python
g.node[n]['mean color'] = (g.node[n]['total color'] /
                           g.node[n]['pixel count'])
```