diff --git a/modules/ui/fci/config.el b/modules/ui/fci/config.el
index 5aaf50ef3..424faae2c 100644
--- a/modules/ui/fci/config.el
+++ b/modules/ui/fci/config.el
@@ -1,12 +1,28 @@
 ;;; ui/fci/config.el -*- lexical-binding: t; -*-
 
+(defvar +fci-rule-color-function
+  (lambda () (face-foreground 'line-number))
+  "Color used to draw the fill-column rule.
+
+Accepts a color string or a function that returns a color.
+
+Changes to this variable do not take effect until `fci-mode' is restarted.")
+
+
+;;
+;; Plugins
+;;
+
 (def-package! fill-column-indicator
   :hook ((text-mode prog-mode conf-mode) . turn-on-fci-mode)
   :config
   (defun +fci|set-color ()
-    (setq fci-rule-color (face-foreground 'line-number)))
-  (add-hook 'doom-load-theme-hook #'+fci|set-color)
-  (+fci|set-color)
+    "Automatically change `fci-rule-color' based on `+fci-rule-color-function's
+return value. To disable this, either set `+fci-rule-color-function' to nil or
+remove `+fci|set-color' from `fci-mode-hook'."
+    (when (functionp +fci-rule-color-function)
+      (setq fci-rule-color (funcall +fci-rule-color-function))))
+  (add-hook 'fci-mode-hook #'+fci|set-color)
 
   (when (featurep! :completion company)
     (add-hook 'company-completion-started-hook #'+fci|disable-when-company-activates)