Document color schemes

[huddlej]

Context

At the beginning of the pandemic, Trevor created a collection of color schemes that could scale to hundreds of categorical values. These color schemes were originally used to generate colors for geographic regions, but they have become handy for more general use throughout ncov analyses (and elsewhere).

Description

We should document where the color schemes file resides and how to use it for primary use cases (like assigning colors to a for custom metadata column associated with a manuscript, etc.).

Possible solution

For example, we could at least link out to the color schemes file, list the hex values up to 10 colors, and then show Python code for how to use these colors in a matplotlib figure or the like.

[jameshadfield]

One limitation of the current ncov workflow (and nextstrain more generally) is that all custom colours have to be specified in one file to be passed to augur export. For example, if you want to use our provided (ordered) colours for country, pango lineage etc, but add in some custom colours then there's no easy way to do this (if you're happy with our colours and simply want to change the ordering or add new values, you can modify ./defaults/color_ordering.tsv but this isn't very nice). This relates to the "data curation" framework we've been talking about, where I'd want to make it easy to define colours independently for different metadata (but without having to keep track of lots of TSVs!).