Coloring Regular Expression via Modus Themes for Treesit Faces

Adding a Bit More Color to My Baseline Theme

In this post, I want to show how I added a bit of additional color to my theme for faces assigned by the built-in Emacs 📖 29 treesit package.


adopting Emacs, I have used the Modus Themes. I appreciate Protesilaos Stavrou (Prot 📖)’s focus on accessibility for the Modus Themes as well as a commitment to accessible documentation.

When you dive deeper into the Modus Themes, you see how customizable and extensible the themes are. I suspect it could be used as a theme-building framework.

In Adding Consistent Color to Emacs Mode Line and iTerm Tab for Various Projects, I showed one way that I’m leveraging Modus Themes to set my mode-line and iTerm2 tab colors by project.

My Emacs Configuration

I’m favoring treesit modes over other modes as Tree Sitter 📖 provides a more robust syntax highlighting.

Below is my treesit and treesit-auto configuration. The treesit package is part of Emacs 29. The treesit-auto package provides automatic translations from non-treesit modes to their corresponding treesit modes. A very helpful package to help bridge other packages that assume one language mode (e.g. ruby-mode) when treesit sets it to a different mode (e.g. ruby-ts-mode).

(use-package treesit
  :custom (treesit-font-lock-level 4)
  :straight (:type  built-in))

(use-package treesit-auto
  :straight (:host github :repo "renzmann/treesit-auto")
  :config (setq treesit-auto-install 'prompt)

Next is the code I use to set my modus-theme. I prefer the “tinted” variation as the day mode (e.g. “operandi”) it’s a bit gentler on my eyes. Most importantly is using modus-themes-load-theme, as that is the function that calls the modus-themes-after-load-theme-hook. More on that in a bit.

(defun jf/emacs-theme-by-osx-appearance ()
  "Set theme based on OSX appearance state."
  (if (equal "Dark" (substring
                      "defaults read -g AppleInterfaceStyle")
                     0 4))
      (modus-themes-load-theme 'modus-vivendi-tinted)
    (modus-themes-load-theme 'modus-operandi-tinted)))


I used the describe-text-properties function to inspect the opening regular expression character. It had the font-lock-regexp-face face.

Likewise, I did the following for Ruby’s string interpolation function (e.g. #{}). That had the face of font-lock-misc-punctuation-face.

Following the Modus Themes documentation, I added the code for setting the foreground color.

(defun jf/modus-themes-custom-faces ()
       ((,c :foreground ,green-warmer)))
       ((,c :foreground ,red-cooler))))))

(add-hook 'modus-themes-after-load-theme-hook

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