Originally, this was a Lua port of chriskempson/base16-vim for Neovim. As base16-vim now appears to be abandonware, the new upstream is considered to be tinted-vim (itself, a fork of base16-vim).
These schemes are implemented in pure Lua, using the lowest-level API for creating highlight groups (vim.api.nvim_set_hl), so as to have the minimum possible impact on startup time.
Originally, this was a base16 theme, but is now a base24 theme (ie. with seven additional colors corresponding to the ANSI "bright" colors). For now, there are no plans to change the name.