Tweak to see if we can get the new colour picking code working

I think the bug in the old code is in it calling reuse or reset colours too often.

I also wanted to pick distinctive colours to make any debugging of colour picking easier.

Here's an example pbo now:
![toll](https://f.cloud.github.com/assets/223723/1649661/c08a2f5a-5a19-11e3-922f-119ab7336de8.png)