diff --git a/crates/ui-egui/src/field_tests.rs b/crates/ui-egui/src/field_tests.rs
index 566f0828b..63995fc80 100644
--- a/crates/ui-egui/src/field_tests.rs
+++ b/crates/ui-egui/src/field_tests.rs
@@ -1194,3 +1194,44 @@ fn sidebar_field_text_stays_in_place_on_focus() {
         assert!((before.center().y - after.center().y).abs() <= 0.5, "numeric={numeric}: before={before:?}, after={after:?}");
     }
 }
+
+/// The Page section's opacity field edits the page background's alpha (#1748; it was a label),
+/// one undo step per commit, and the hex field keeps that opacity unless the typed colour
+/// carries its own.
+#[test]
+fn the_page_background_opacity_field_sets_the_page_colour_alpha() {
+    let mut u = Ui::new(Session::new());
+    u.ctx.enable_accesskit();
+    u.frame(vec![]);
+    let page_bg = |u: &Ui| {
+        let page = u.app.session.page().unwrap();
+        match &u.app.session.doc().unwrap().node(page).unwrap().kind {
+            figcraft_doc::NodeKind::Page { background, .. } => *background,
+            _ => panic!("the page"),
+        }
+    };
+    // Within an 8-bit step: the colour travels as RRGGBBAA.
+    let near = |a: f32, b: f32| (a - b).abs() < 1.0 / 255.0;
+    assert!(near(page_bg(&u).a, 1.0));
+    let steps = undo_steps(&u);
+    type_into(&mut u, "Opacity", "50", Key::Enter);
+    assert!(near(page_bg(&u).a, 0.5), "{:?}", page_bg(&u));
+    assert_eq!(undo_steps(&u), steps + 1, "one undo step for the commit");
+    // The hex field keeps the opacity when the typed colour has none, and takes one it carries.
+    let hex = |u: &mut Ui| u.ctx.read_response(Id::unique("pagebg").with("click")).expect("the hex field").rect.center();
+    let at = hex(&mut u);
+    click(&mut u, at);
+    u.frame(vec![Event::Text("FF0000".into())]);
+    key(&mut u, Key::Enter, Modifiers::NONE);
+    let c = page_bg(&u);
+    assert!(near(c.r, 1.0) && near(c.g, 0.0) && near(c.a, 0.5), "{c:?}");
+    let at = hex(&mut u);
+    click(&mut u, at);
+    u.frame(vec![Event::Text("00FF0080".into())]);
+    key(&mut u, Key::Enter, Modifiers::NONE);
+    let c = page_bg(&u);
+    assert!(near(c.g, 1.0) && near(c.a, 128.0 / 255.0), "{c:?}");
+    assert_eq!(undo_steps(&u), steps + 3);
+    u.app.run("edit.undo", json!({}));
+    assert!(near(page_bg(&u).r, 1.0) && near(page_bg(&u).a, 0.5), "undo takes back the last colour alone");
+}
diff --git a/crates/ui-egui/src/panels/right.rs b/crates/ui-egui/src/panels/right.rs
index 6dde13136..4f31f4089 100644
--- a/crates/ui-egui/src/panels/right.rs
+++ b/crates/ui-egui/src/panels/right.rs
@@ -311,27 +311,48 @@ fn design(app: &mut FigApp, ui: &mut Ui) {
 /// Draw the page section: background and colour profile, local variables/styles, and the
 /// page export section.
 fn page_section(app: &mut FigApp, ui: &mut Ui, doc: &Document) {
-    let t = Tokens::get(ui.ctx());
     let Ok(page) = app.session.page() else { return };
     let bg = match doc.node(page).map(|n| &n.kind) {
         Some(NodeKind::Page { background, .. }) => *background,
         _ => figcraft_color::Color::DEFAULT_PAGE,
     };
     widgets::section_header(ui, tr("Page"), &[], false);
-    let mut new_hex = None;
+    // The new colour and, from a scrub, whether the scrub is over (live edits stay one undo step).
+    let mut new_color: Option<(figcraft_color::Color, Option<bool>)> = None;
     row(ui, 32.0, |ui| {
         let p = Paint::solid(bg);
         let sw = widgets::swatch(ui, &p, 16.0);
         app.picker_control(crate::colorpicker::PickerTarget::PageBackground, &sw);
-        if let Some(h) = widgets::text_field(ui, Id::unique("pagebg"), &bg.to_hex(), 96.0, "") {
-            new_hex = Some(h);
+        // A typed colour keeps the page's opacity unless it carries one (`FF000080`), as the
+        // colour picker's hex field does.
+        if let Some(h) = widgets::text_field(ui, Id::unique("pagebg"), &bg.to_hex(), 96.0, "")
+            && let Some(c) = figcraft_color::Color::from_hex_or_name(&h)
+        {
+            new_color = Some((c.with_alpha(if c.a < 1.0 { c.a } else { bg.a }), None));
+        }
+        // The opacity: a field like every other opacity field, not a label (#1748).
+        let alpha = |v: f64| bg.with_alpha((v / 100.0).clamp(0.0, 1.0) as f32);
+        let shown = Some(f64::from((bg.a * 100.0).round()));
+        match widgets::number_field(ui, Id::unique("pagebg_a"), Lead::Named(tr("Opacity")), shown, "%", 56.0, 1.0) {
+            Some(FieldEdit::Set(v)) => new_color = Some((alpha(v), None)),
+            Some(FieldEdit::Scrub(v, done)) => new_color = Some((alpha(v), Some(done))),
+            None => {}
         }
-        widgets::label(ui, "100 %", t.text);
     });
-    if let Some(h) = new_hex
-        && let Some(c) = figcraft_color::Color::from_hex_or_name(&h)
-    {
-        app.run("page.setBackground", json!({"color": c.to_css_hex()}));
+    if let Some((c, scrub)) = new_color {
+        let p = json!({"color": c.to_css_hex()});
+        match scrub {
+            None => {
+                app.run("page.setBackground", p);
+            }
+            Some(done) => {
+                let _ = app.session.begin_interaction("Page background");
+                let _ = app.session.execute("page.setBackground", &p);
+                if done {
+                    let _ = app.session.commit_interaction();
+                }
+            }
+        }
     }
     widgets::separator(ui);
     widgets::section_header(ui, tr("Color profile"), &[], false);