Normalize colour values

This normalizes all of the colour values across the site with our new vocabulary, and gets rid of references to all old values. 

```$c-neutral6``` is the new ```$medianMushroom``` 



![colours](https://f.cloud.github.com/assets/80089/1282001/0496bbec-2f6c-11e3-9c3f-63972fceca86.png)