diff --git a/src/shaders/glsl/natural-mystic-hacks.h b/src/shaders/glsl/natural-mystic-hacks.h
index 3021d5c..ac41c3f 100644
--- a/src/shaders/glsl/natural-mystic-hacks.h
+++ b/src/shaders/glsl/natural-mystic-hacks.h
@@ -6,10 +6,22 @@
 
 /* Detect leaves based on the color of material. */
 bool isLeaf(vec4 color) {
+    /* FIXME: This function currently fails to detect leaves whose
+     * color is affected by seasons. */
     vec4 norm = normalize(color);
     return norm.g >= 0.65 && norm.g <= 0.9;
 }
 
+/* Detect grasses based on the color of material. This function also
+ * returns true for grass blocks and leaves because it's impossible to
+ * tell them from plants. [Currently unused]
+ */
+bool isGrass(vec4 color) {
+    /* Grass colors are affected by seasons and can turn red. */
+    vec4 hsv = rgb2hsv(color);
+    return hsv.x >= 149.0 && hsv.x <= 270.0;
+}
+
 /* Detect water based on the color of material. */
 bool isWater(vec4 color) {
     /* Yikes. The color of water greatly changes in swampland so we