I'm not sure if eddyg had a different idea, but I think the following sums it up:

  - base16 is a specification of how different UI elements map to colors [1], and also some tooling, configuration files, etc. to automate setting this up for many different applications.
  - For a user to be able to use base16 with a tool, either:
    - Allow the user to set their preferred colors for UI elements at a semantic level, preferrably in a config file, and even more preferrably in a separate file that can be included into the main config file so that it's easier to automate (i.e. I have a separate `colors.sh` that is loaded in my `.zshrc`).
    - Let the user set their shell colors however they want (presumably using [2]), and use the ANSI shell colors (and a few more) according to the base16 style guide [1]. Some translation between shell colors and base16 colors will be necessary, e.g. base16 says that a language keyword should use the color base0E, which in [2] corresponds to ANSI shell color 13.

My impression is that the base16 specification is not sufficiently general for most tools to implement it in a totally unbambiguous way, but if users can set their own colorschemes with a config file, it's not hard for a user to come up with a base16-approximating colorscheme template file, from which other users can generate a config file that sets a specific base16 colorscheme.

[1]: https://github.com/chriskempson/base16/blob/main/styling.md [2]: https://github.com/chriskempson/base16-shell