Update generate.py

1. changed color map to blues. 
2. colour bar is reversed by Blues_r except on the colour bar at bottom left so as to cope with my rather unintuitive motion scoring system so darker hues represent greater motion.
3. so now need to somehow fix it at 6 plots per page (88 subjects in full dataset)
4. where in the code can i set the page background colour?
![left_ventricle_bulls_eyes_ aha _group_2](https://cloud.githubusercontent.com/assets/9017257/4534614/d5160390-4da7-11e4-9f96-e4bd7a9f6416.png)