diff --git a/crates/algo/src/artistic.rs b/crates/algo/src/artistic.rs
index 5aab3564..42660914 100644
--- a/crates/algo/src/artistic.rs
+++ b/crates/algo/src/artistic.rs
@@ -147,9 +147,12 @@ impl GalleryFilter {
         out
     }
 
-    /// Whether the filter reads the foreground / background colours.
+    /// Whether the filter reads the foreground / background colours. Derived
+    /// from the params notation, plus the filters whose pixel code reads the
+    /// colours without listing them (issue #709): Colored Pencil uses the
+    /// background as paper tint, Neon Glow mixes foreground over background.
     pub fn uses_colours(self) -> bool {
-        self.params_doc().contains("\"foreground\"") || self.params_doc().contains("\"background\"")
+        matches!(self, Self::ColoredPencil | Self::NeonGlow) || self.params_doc().contains("\"foreground\"") || self.params_doc().contains("\"background\"")
     }
 }
 
diff --git a/crates/engine/tests/gallery_colours.rs b/crates/engine/tests/gallery_colours.rs
new file mode 100644
index 00000000..d1561e8a
--- /dev/null
+++ b/crates/engine/tests/gallery_colours.rs
@@ -0,0 +1,33 @@
+//! Regression tests for issue #709: the single-filter gallery commands must
+//! record the session foreground/background colours for every filter that
+//! reads them. Colored Pencil (background) and Neon Glow (both) read the
+//! colours in their pixel code but omit them from their params notation, so
+//! the injection was skipped and they always ran with the defaults.
+use photocraft_engine::Session;
+use serde_json::json;
+
+fn px(s: &mut Session, x: i32, y: i32) -> Vec<f32> {
+    serde_json::from_value(s.execute("document.pixel", json!({"x": x, "y": y})).unwrap()).unwrap()
+}
+
+fn image(s: &mut Session) -> Vec<f32> {
+    (0..16).flat_map(|y| (0..16).map(move |x| (x, y))).flat_map(|(x, y)| px(s, x, y)).collect()
+}
+
+fn one(filter: &str, bg: &str) -> Vec<f32> {
+    let mut s = Session::new();
+    s.execute("file.new", json!({"width": 16, "height": 16, "background": "#808080"})).unwrap();
+    s.execute("tools.setColors", json!({"background": bg})).unwrap();
+    s.execute(&format!("filter.gallery.{filter}"), json!({})).unwrap();
+    image(&mut s)
+}
+
+#[test]
+fn colored_pencil_honours_session_background() {
+    assert_ne!(one("coloredPencil", "#ffffff"), one("coloredPencil", "#0000ff"), "filter.gallery.coloredPencil must honour the session background");
+}
+
+#[test]
+fn neon_glow_honours_session_background() {
+    assert_ne!(one("neonGlow", "#ffffff"), one("neonGlow", "#0000ff"), "filter.gallery.neonGlow must honour the session background");
+}