diff --git a/bin/greyscale b/bin/greyscale
new file mode 100755
index 0000000..092a87a
--- /dev/null
+++ b/bin/greyscale
@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+#
+# Grayscale using picom.
+# Based on https://wiki.archlinux.org/title/Picom#Grayscale
+
+killall picom
+    picom --backend glx --glx-fshader-win "
+      uniform float opacity;
+      uniform bool invert_color;
+      uniform sampler2D tex;
+
+      void main() {
+        vec4 c = texture2D(tex, gl_TexCoord[0].xy);
+        float g = (c.r + c.g + c.b) / 3.0;  // EDIT1: Average.
+        c = vec4(vec3(g), c.a);  // EDIT2: Color.
+        if (invert_color)
+          c = vec4(vec3(c.a, c.a, c.a) - vec3(c), c.a);
+        c *= opacity;
+        gl_FragColor = c;
+      }
+    "