Read Mode: a Page color menu shows the columns on white, sepia or a dark page

Word's Read Mode has View › Page Color with None, Sepia and Inverse.
The Read Mode toolbar now has a Page color menu beside Line spacing,
backed by the view.readPageColor command. None draws the columns on
white and does not show the document's page color or page picture.
Sepia draws them on Word's sepia paper (RGB 112, 66, 20 at 80%
transparency over white) and leaves the text's colors alone. Inverse
draws the dark page that View › Switch Modes draws.

The setting is screen only, is not saved, and starts at None on each
entry to Read Mode, as the other reading controls do. In Read Mode it
sets the paper even while Switch Modes is on. Print Layout and the
other views still show the document's page color, and Switch Modes
still darkens them.

crates/engine/src/cmd/view.rs

@@ -37,6 +37,9 @@ pub fn specs() -> Vec<CommandSpec> {
         CommandSpec::new("view.readLineSpacing", "Reading Line Spacing", "Reading › Layout", read_line_spacing)
             .params(r#"{"value": "document" | 1.0 | 1.25 | 1.5 | 2.0}"#)
             .pure(),
+        CommandSpec::new("view.readPageColor", "Reading Page Color", "Reading › Layout", read_page_color)
+            .params(r#"{"value": "none" | "sepia" | "inverse"}"#)
+            .pure(),
         // Print Layout: hide the white space (margins, headers, footers) between pages. Screen only.
         CommandSpec::new("view.hideWhiteSpace", "Hide White Space", "View › Show", |s, v| toggle(s, v, |x| &mut x.hide_white_space))
             .params(r#"{"value"?: bool}"#)
@@ -171,6 +174,7 @@ fn mode(s: &mut Session, m: ViewMode, read: bool) -> CmdResult {
         s.view.read_column_width = None;
         s.view.read_zoom = 1.0;
         s.view.read_line_spacing = None;
+        s.view.read_page_color = ReadPageColor::None;
     }
     s.view.mode = m;
     s.view.read_mode = read;
@@ -213,6 +217,31 @@ fn read_line_spacing(s: &mut Session, v: &Value) -> CmdResult {
     Ok(json!({"spacing": spacing}))
 }
 
+/// Read Mode › View › Page Color, as in Word. Screen only: the document and its own page color
+/// are unchanged.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub enum ReadPageColor {
+    /// White paper; the document's page color and page picture are not shown.
+    #[default]
+    None,
+    /// Sepia paper (Word's RGB 112, 66, 20 at 80% transparency over white); the text keeps its colors.
+    Sepia,
+    /// A dark page with light text, as View › Switch Modes draws it.
+    Inverse,
+}
+
+fn read_page_color(s: &mut Session, v: &Value) -> CmdResult {
+    let color = match v.get("value").and_then(Value::as_str) {
+        Some("none") => ReadPageColor::None,
+        Some("sepia") => ReadPageColor::Sepia,
+        Some("inverse") => ReadPageColor::Inverse,
+        _ => return Err(CmdError::Params("reading page color must be none, sepia, or inverse".into())),
+    };
+    s.view.read_page_color = color;
+    Ok(json!({"pageColor": color}))
+}
+
 /// The zoom a document is saved with (#995): the fit mode, else the percentage; `None` at 100%.
 pub(crate) fn saved_zoom(v: &crate::ViewState) -> Option<Zoom> {
     let fit = match v.fit.as_str() {

crates/engine/src/session.rs

@@ -178,6 +178,9 @@ pub struct ViewState {
     pub read_zoom: f32,
     #[serde(skip)]
     pub read_line_spacing: Option<f32>,
+    /// Read Mode's Page Color: the paper the reading columns are drawn on.
+    #[serde(skip)]
+    pub read_page_color: crate::cmd::view::ReadPageColor,
     pub dark_mode: bool,
     pub show_markup: bool,
     pub track_changes_pane: bool,
@@ -265,6 +268,7 @@ impl Default for ViewState {
             read_column_width: None,
             read_zoom: default_read_zoom(),
             read_line_spacing: None,
+            read_page_color: Default::default(),
             dark_mode: false,
             show_markup: true,
             track_changes_pane: false,

crates/engine/src/tests.rs

@@ -5181,6 +5181,32 @@ fn reading_mode_reflows_per_viewport_without_changing_document_or_export() {
     assert_eq!(s.view.read_line_spacing, None);
 }
 
+/// Read Mode › View › Page Color: None, Sepia or Inverse, a view setting that leaves the
+/// document alone, is not saved, and starts at None on each entry to Read Mode.
+#[test]
+fn reading_page_color_is_a_transient_view_setting() {
+    use crate::cmd::view::ReadPageColor;
+    let mut s = s();
+    let original = s.doc.clone();
+    let dirty = s.dirty;
+    run(&mut s, "view.readMode", json!({}));
+    assert_eq!(s.view.read_page_color, ReadPageColor::None);
+    assert_eq!(s.run("view.readPageColor", &json!({"value": "sepia"})).unwrap(), json!({"pageColor": "sepia"}));
+    assert_eq!(s.view.read_page_color, ReadPageColor::Sepia);
+    run(&mut s, "view.readPageColor", json!({"value": "inverse"}));
+    assert_eq!(s.view.read_page_color, ReadPageColor::Inverse);
+    for bad in [json!({"value": "black"}), json!({"value": 1}), json!({})] {
+        assert!(s.run("view.readPageColor", &bad).is_err(), "{bad}");
+    }
+    assert_eq!(s.view.read_page_color, ReadPageColor::Inverse, "rejected values keep the color");
+    assert!(serde_json::to_value(&s.view).unwrap().get("readPageColor").is_none());
+    assert_eq!(s.doc, original);
+    assert_eq!(s.dirty, dirty);
+    run(&mut s, "view.printLayout", json!({}));
+    run(&mut s, "view.readMode", json!({}));
+    assert_eq!(s.view.read_page_color, ReadPageColor::None);
+}
+
 /// File › Options › Advanced › Numeral: the display mode for digits (display only).
 #[test]
 fn numeral_mode_sets_gets_and_rejects_junk() {