niri: make focus ring the inverse of the average of the background color

home-manager/progs/niri.nix

@@ -5,6 +5,9 @@
   inputs,
   ...
 }:
+let
+  invert_image_avg = pkgs.callPackage ../util/inverse_color.nix;
+in
 {
   imports = [
     inputs.niri.homeModules.config
@@ -51,7 +54,9 @@
         focus-ring = {
           enable = true;
           active = {
-            color = "#bf7778";
+            color = builtins.readFile (invert_image_avg {
+              src = ../wallpaper.png;
+            });
           };
         };
       };