onedark.nvim is a Neovim 0.9+ colorscheme plugin implementing the Atom One Dark and One Light themes with Lua and TreeSitter support. The codebase provides 8 theme styles (dark, darker, cool, deep, warm, warmer, light), comprehensive TreeSitter highlight definitions (modern @-prefixed captures), LSP semantic token integration, and support for over 24 plugins (nvim-cmp, telescope, lualine, indent-blankline, etc.). It includes a robust test suite with automated highlight group verification and manual visual testing files. The architecture is modular: palette.lua defines raw color values per style, colors.lua selects and merges with user overrides, highlights.lua maps groups to colors with configurable code styles (italic, bold), and init.lua handles setup/loading/toggling. The utility module provides reusable color blending functions. The repository is actively maintained with frequent releases, detailed changelogs, and responsive issue triage. While primarily a Neovim plugin, its color handling and test patterns could inspire similar theme implementations.