Improve colour distinction metric

[jack89roberts]

My impression is that different shades of green are favoured a bit too much at the moment.

[jack89roberts]

Relevant references/similar work:

• https://strathprints.strath.ac.uk/30312/1/colorpaper_2006.pdf
• https://github.com/holoviz/colorcet
• https://github.com/taketwo/glasbey