mix colors for hybrid recoding strategies (dragoon/komodo!112)

- define `scripts/color.nu` to manipulate RGB colors, especially mix two colors together
- compute the color of _hybrid recoding strategies_ as a weighted sum of the two _simple recoding strategies_ involved, e.g. if the strategy is "10% of the time recode 2 shards and 90% of the time recode 3", then the color of that curve will be 10% the color of the simple strategy recoding 2 shards and 90% the color of the other simple strategy recoding 3 shards
- make the _hybrid_ curves transparent and dashed

## example
![foo](/uploads/71afca07a87fc38e3fa005cebfab4e50/foo.png)