Artboards: each artboard can have a background color on the canvas

Squashed from #2403 onto main.

docs/gaps.md

@@ -239,6 +239,8 @@ from G14 and the budget run of G15: **~170–270 h** one agent, ~50–80 h wall
 ## G13 Illustrator 2026 (30.x) additions
 
 - **Done:** TIFF choices and format settings in Export for Screens and Asset Export (30.2), using the existing encoder; UI-to-file regressions cover selection, scaling, options and persistence.
+- **Done:** artboard background colors on the canvas (30.0): Properties › Artboards › Fill and Artboard Options set
+  each artboard's color, and the canvas draws its paper in it. Exports and print do not draw the color yet.
 
 - **Done:** Object › Intertwine (#1763): Make, Edit and Release; the Intertwine tool highlights the overlap area under
   the pointer, a click swaps which object is on top there, and a path (Shift: a rectangle) drawn around overlaps
@@ -252,7 +254,7 @@ from G14 and the budget run of G15: **~170–270 h** one agent, ~50–80 h wall
 - **Missing (asked for by users, from earlier versions):** radial gradients in Image Trace's
   Gradients option, which traces linear ones only (draft #1849). Inside the estimate below.
 - **Missing:** gradient dither and perceptual blending, gradient presets (30.0); tangent and perpendicular
-  snapping and the consolidated snapping options (30.0); artboard locking, artboard colours and managing
+  snapping and the consolidated snapping options (30.0); artboard locking, artboard colors in exports and print, and managing
   artboards from the canvas (30.0); the Blend panel with ease in/out and separate colour acceleration (30.7);
   the Dimension tool (28.x).
 - **Evidence:** Adobe's 30.0 and 30.7 release announcements, see

docs/mcp.md

@@ -350,7 +350,7 @@ objects' fills or strokes differ (`fillMixed` / `strokeMixed`, drawn as a "?" pr
 |---|---|---|
 | `list_commands` | `{filter?, query?, menu?, enabledOnly?, brief?}` | The command catalogue: id, label, menu, shortcut, params doc (left out with `brief`), enablement. |
 | `run_command` | `{command, params?}` | Runs any command. Use it for everything without a dedicated tool. |
-| `inspect_document` | `{depth?, childLimit?, ids?, kind?, limit?, offset?}` | Artboards, layer tree (ids, kinds, bounds, paint), selection, history, tool. A type node's `fill`, `stroke` and `strokeWidth` are the paint its characters show (its first run's); fills and strokes of the type object itself come as `objectFill`, `objectStroke` and `objectStrokeWidth`. Paint comes as a label (`"#ff0000"`, `"None"`, `"G1 40% (#ff9999)"` for a swatch at a tint); `paint.proxies` gives it as an object. |
+| `inspect_document` | `{depth?, childLimit?, ids?, kind?, limit?, offset?}` | Artboards (with `color`, `#rrggbb`, for one with a background color), layer tree (ids, kinds, bounds, paint), selection, history, tool. A type node's `fill`, `stroke` and `strokeWidth` are the paint its characters show (its first run's); fills and strokes of the type object itself come as `objectFill`, `objectStroke` and `objectStrokeWidth`. Paint comes as a label (`"#ff0000"`, `"None"`, `"G1 40% (#ff9999)"` for a swatch at a tint); `paint.proxies` gives it as an object. |
 | `inspect_ui` | `{}` | UI state. Remote mode only. |
 | `select_tool` | `{tool}` | `selection`, `directSelection`, `pen`, `rectangle`, `ellipse`, `polygon`, `star`, `lineSegment`, … |
 | `pointer_gesture` | `{events:[{kind,x,y,mods?}], tool?, mods?}` | `kind` is one of `down`, `drag`, `up`, `move`, `doubleclick`. Events go through the same path as the mouse. |
@@ -2738,7 +2738,7 @@ value: true}`; the Control bar's and Properties' Scale Artwork with Artboard che
 Artboard) makes its handle drags proportional and passes `scaleArt`, as do Properties' and the Transform panel's
 artboard size fields while the tool is in use.
 
-`artboard.setProps {artboards: [{index, name?, x?, y?, width?, height?}…], scaleArt?, moveArt?, …}` sets several
+`artboard.setProps {artboards: [{index, name?, color?, x?, y?, width?, height?}…], scaleArt?, moveArt?, …}` sets several
 artboards in one undo step, each with its own fields; the other params apply to all of them. The art that moves or
 scales with each artboard is the art inside it before any of them changes, and an object inside several of them goes
 with the first one listed that moves or scales its art. An empty list and a list that names an artboard twice are
@@ -2758,6 +2758,15 @@ artboard only, and Artboard Options' Name renames only the artboard it shows.
 {"name":"run_command","arguments":{"command":"artboard.setProps","params":{"artboards":[{"index":0,"width":300},{"index":2,"width":300}],"scaleArt":true}}}
 ```
 
+An artboard's background color (Properties › Artboards › Fill, Artboard Options' Background Color): `artboard.setProps
+{index, color}` sets it, with a color as the paint commands take it (`"#rrggbb"`, `{c, m, y, k}`, …), and
+`artboard.setProps {index, color: null}` removes it, each in one undo step; `artboard.new {color}` makes an artboard
+with one. The canvas draws that artboard's paper in
+the color. With Simulate Colored Paper on, it multiplies the color with the paper color, each sRGB channel as
+artboard × paper / 255; artboards without a color show the paper color. The transparency grid still covers it while
+it shows. Copies, duplicates and the native format keep the color; exports and print do not draw it. `inspect_document`
+lists it as the artboard's `color` (`#rrggbb`), and `ui.colorPicker {artboard: index}` opens the Color Picker for it.
+
 ```json
 {"name":"run_command","arguments":{"command":"artboard.copy","params":{"index":0}}}
 {"name":"run_command","arguments":{"command":"edit.paste","params":{}}}

docs/target-app-parity.md

@@ -435,6 +435,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
 - **Names of new and renamed artboards, brushes and patterns:** `artboard.new` and `artboard.setProps` trim the white space around the name they are given, as the Artboards panel's rename does, and a blank name gives the artboard its default name, Artboard N for the Nth artboard. `brush.new`, `brush.duplicate`, `brush.options`, `object.pattern.make`, `object.pattern.saveCopy` and `pattern.options` trim the name as the Brush Options dialog and the Pattern Options panel do, and compare the trimmed name with the names there are; a blank name gives the name each command gives when there is none, and Brush Options and Pattern Options keep the name. Tests in `tests_panelcmds.rs`, `tests_brushsym.rs` and `tests_pattern.rs` cover each command. Public references: [Using multiple artboards](https://web.archive.org/web/20210925094818/https://helpx.adobe.com/illustrator/using/using-multiple-artboards.html), [Brushes](https://web.archive.org/web/20251018101754/https://helpx.adobe.com/illustrator/using/brushes.html) and [Create and edit patterns](https://web.archive.org/web/20211031180358/https://helpx.adobe.com/illustrator/using/create-edit-patterns.html) (archived copies).
 - **Pattern names and swatch names:** `pattern.options` refuses a new name that another pattern, a swatch or a color group has. It takes a name that only the pattern's own swatches have. The reference page does not say what happens when the new name is taken; the refusal follows VectorCraft's rule that swatches and color groups share one namespace (`Document::swatch_name_taken`), which `swatch.new` and `swatch.edit` also follow. A rename gives the new name only to the pattern's swatches that had the old one; any other swatch with the old name keeps it, and art linked to that swatch stays linked. `object.pattern.make` and `object.pattern.saveCopy` number a color group's name as they number a swatch's. Tests in `tests_pattern.rs` cover each command. Public reference: [Create and edit patterns](https://web.archive.org/web/20211031180358/https://helpx.adobe.com/illustrator/using/create-edit-patterns.html) (archived copy).
 - **Edit Artboards in Properties:** the active artboard's name is a field. Typing a new name and pressing Enter or clicking elsewhere renames that artboard in one undo step, as the Artboards panel's rename does (`artboard.setProps {index, name}`); pressing Escape or leaving the field empty keeps the old name. A click on the Artboard Options icon beside the field opens Artboard Options for the active artboard, as double-clicking the Artboard tool's button does (`tool.options {tool: "artboard"}`). Pointer and key tests in `panels/properties.rs` cover both. Public references: [Resize artboards](https://helpx.adobe.com/illustrator/desktop/create-manage-artboards/add-edit-artboards/resize-artboards.html) and [Create and add new artboards](https://helpx.adobe.com/illustrator/desktop/create-manage-artboards/add-edit-artboards/add-new-artboards.html).
+- **Artboard background colors:** each artboard can have a background color (`artboard.setProps {index, color}`, `color: null` removes it). With the Artboard tool, Properties has a Fill row: its list sets None, White or Black, and its chip and its Color Picker… item open the Color Picker for the artboard. Artboard Options has a Background Color row with a list that sets None, White or Black, and a color button. The canvas draws the artboard's paper in the color, multiplied with the paper color while Simulate Colored Paper is on, and the transparency grid still covers it. The native format saves the color, and a document without colors saves as before. Exports and print do not draw the color. Engine, canvas, Properties, Color Picker and Artboard Options tests cover it. Public reference: [Apply colors to artboards](https://helpx.adobe.com/illustrator/desktop/create-manage-artboards/organize-manage-artboards/add-background-color-to-artboards.html).
 - **Resizing several artboards:** with several artboards selected with the Artboard tool, a new W or H in Properties, the Transform panel or the Control bar, a preset or an orientation in Properties or the Control bar, and a new Width or Height in Artboard Options resize every selected artboard in one undo step (`artboard.setProps {artboards}`); with Scale Artwork with Artboard on, Properties, the Transform panel and the Control bar scale each object once, with the artboard it was inside before the change. The Transform panel, the Control bar and Artboard Options resize each one about its own reference point, a preset sizes each one in its own orientation, and X and Y still move the active artboard alone. Pointer and key tests in `panels/properties.rs`, dialog tests in `dialogs/tests.rs` and an engine test in `tests_xform.rs` cover them. Public references: [Artboard Enhancements In Illustrator CC](https://blog.adobe.com/en/publish/2017/11/10/artboard-enhancements-in-illustrator-cc) ("modify them all in bulk by defining the height and width values") and [Using multiple artboards](https://helpx.adobe.com/illustrator/using/using-multiple-artboards.html) (2019).
 - **Artboard Escape routing:** Escape leaves Artboard editing for Selection; during a drag it first cancels the gesture. Headless egui key events cover idle Escape, active-drag cancellation and a subsequent Escape in `tests_distortkeys.rs`.
 - **Shift with the Artboard tool:** a Shift-click adds an artboard to the selection or takes it out when the button comes up. A Shift-drag inside an artboard draws a new artboard there, and a Shift-drag on the pasteboard is a marquee that toggles the artboards it touches, as the [default keyboard shortcuts](https://helpx.adobe.com/illustrator/using/default-keyboard-shortcuts.html) ("Create artboard inside another artboard") and [Using multiple artboards](https://web.archive.org/web/20210925094818/https://helpx.adobe.com/illustrator/using/using-multiple-artboards.html) (archived copy) describe. Shift no longer keeps an artboard move at 45° steps or a drawn artboard square. Escape during a marquee or while a new artboard is being drawn cancels it and keeps the Artboard tool. Pointer and key tests in `crates/tools/src/xform/artboard.rs` cover the four gestures and Escape.