diff --git a/crates/ui-egui/src/canvas.rs b/crates/ui-egui/src/canvas.rs
index 3d78f952d..a79724306 100644
--- a/crates/ui-egui/src/canvas.rs
+++ b/crates/ui-egui/src/canvas.rs
@@ -26,8 +26,10 @@ const TEXT_TAG: u64 = 1 << 62;
 /// A page rendered for the organize grid at the size it is drawn there.
 const GRID_TAG: u64 = 1 << 61;
 /// Preview rasters tagged with this bit are converted to luminance on receipt, matching the
-/// monochrome print requested by Print ▸ Print in grayscale.
-const GRAYSCALE_TAG: u64 = 1 << 60;
+/// monochrome print requested by Print ▸ Print in grayscale. It is a bit of its own: the
+/// renderer's print bit ([`PRINT_TAG`]) is carried by every print preview, so sharing it would
+/// turn colour previews into monochrome ones too.
+const GRAYSCALE_TAG: u64 = 1 << 59;
 /// The tag of a raster that is out of date (shown until its replacement arrives).
 const STALE_TAG: u64 = u64::MAX;
 /// Pages whose raster would exceed this many device pixels on a side are drawn in tiles.
@@ -5867,6 +5869,25 @@ trailer << /Root 1 0 R >>
         }
     }
 
+    /// A print preview carries the renderer's print bit; the bit that asks for luminance is
+    /// its own, so a colour preview is not converted to monochrome and the two modes are told
+    /// apart by their tags.
+    #[test]
+    fn print_preview_tag_distinguishes_grayscale_from_colour() {
+        let mut v = view(1, PageLayout::Single, true);
+        v.set_print_grayscale(false);
+        v.queue_print_previews(&[(0, 1.0)]);
+        let colour = v.frame_queue.last().expect("a print preview was queued").tag;
+        assert_ne!(colour & PRINT_TAG, 0, "a print preview carries the renderer's print bit");
+        assert_eq!(colour & GRAYSCALE_TAG, 0, "a colour print preview must not ask for luminance");
+
+        v.set_print_grayscale(true);
+        v.queue_print_previews(&[(0, 1.0)]);
+        let gray = v.frame_queue.last().expect("a grayscale print preview was queued").tag;
+        assert_ne!(gray & GRAYSCALE_TAG, 0, "a grayscale print preview asks for luminance");
+        assert_ne!(gray, colour, "the two print preview modes must not share a tag");
+    }
+
     #[test]
     fn thumbnails_release_on_scroll_panel_close_and_request_again_after_eviction() {
         let ctx = egui::Context::default();