How Emacs Helped Me Today: modus-themes and ef-themes Palettes for LaTeX

I’m very fond of Prot’s modus-themes and ef-themes for emacs. They’re highly legible, easy on the eyes, and attractive. Recently I was making a beamer presentation for a talk I’m currently procrastinating on. For better or for worse, I thought to myself I wish I could make the PDF output have modus theme colors.

After manually reading off some colors from modus-operandi-tinted-palette into my LaTeX preamble, I remembered: Wait, this is emacs. There’s a better way to do this.

Happily, Prot designed the modus-themes and ef-themes palettes in simple way; they are just lists of lists with the name and hex value of the color. Here’s an excerpt of modus-operandi-tinted-palette:

((bg-main "#fbf7f0")
 (bg-dim "#efe9dd")
 (fg-main "#000000")
 (fg-dim "#595959")
 (fg-alt "#193668")
 (bg-active "#c9b9b0")
 (bg-inactive "#dfd5cf")
 (border "#9f9690")
 (red "#a60000")
 ... )

It’s easy enough to write a function to read from the palette and generate LaTeX directives for defining (most of) the colors. We want to fill a file with color directives that look like this:

\definecolor{COLOR-NAME}{HTML}{XXXXXX}

Here, the =COLOR-NAME will just be the name of the symbol that the palette gives to a color, and the XXXXXX will be the HTML (hex) code, sans the leading #.

The code I wrote is

(defun gen-emacs-theme-html-latex-colors (theme-palette)
  (pcase-dolist (`(,color-name ,hex) theme-palette)
    (insert
     (concat "\\definecolor{" (symbol-name color-name) "}{HTML}{"))
    (let ((rgb (substring  hex 1)))
      (insert (concat rgb "}\n")))))

All this does is loop through theme-palette, and for each element, insert the LaTeX directive we wanted, separated by newlines. Here’s an excerpt of the generated output for modus-operandi-tinted:

\definecolor{bg-main}{HTML}{fbf7f0}
\definecolor{bg-dim}{HTML}{efe9dd}
\definecolor{fg-main}{HTML}{000000}
\definecolor{fg-dim}{HTML}{595959}
\definecolor{fg-alt}{HTML}{193668}
\definecolor{bg-active}{HTML}{c9b9b0}
\definecolor{bg-inactive}{HTML}{dfd5cf}
\definecolor{border}{HTML}{9f9690}
...

There is a limitation, however. The palette is self referential, meaning the hex color value of some the colors is the symbol of a previously defined color. The function terminates running on these, but at that point, there are something like 119 unique colors already defined, more than enough to make a coherent beamer theme.

Defining the beamer theme is then a matter of using \setbeamercolor commands and change the colors of the desired presentation elements using a guide such as this one. Note also that the ef-themes use the same color palette format, so this function will work exactly the same for them.

Happy scripting!