Select Color and ribbon: ByLayer shows the layer's colour

ByLayer swatches were always gray. The Select Color panel's Current/New
band and info line now show the colour of the layer the colour is for
(the newest selected object's layer, or the current layer for new
objects); the ribbon's colour control and the ByLayer row of its colour
dropdown show the current layer's colour.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013rGmDUNr1hUf4zo1X3dak8

src/ui/ribbon/widgets.rs

@@ -1167,7 +1167,12 @@ pub(super) fn render_large<'a>(item: &RibbonItem, ctx: &RenderCtx<'_>) -> Elemen
                 .width(Length::Fixed(PROP_W))
             };
 
-            let (color_swatch, _) = acad_color_display(active_color);
+            // ByLayer shows the current layer's colour.
+            let color_swatch = layer_infos
+                .iter()
+                .find(|layer| layer.name == active_layer)
+                .filter(|_| active_color == AcadColor::ByLayer)
+                .map_or_else(|| acad_color_display(active_color).0, |layer| layer.color);
             let color_row = prop_row(
                 crate::ui::color_select::color_display_name(active_color),
                 PROP_COLOR_ID,