- Replace the idea of color schemes with the idea of named colors (since none of our colorschemes have used `colorA`)
- Pass through the normalized color to `_shields_test` to harmonize with BaseService and simplify testing
- Update service tests
- Move responsibility for color generation into the npm package
- Remove several color helper functions and their tests
- Update gh-badge public API to accept `color` and `labelColor`
This is a precursor to refactoring some of the logo code for #2473.
