render: the bodies of a design with several in their own colours

Geometry triangles remember their surface (body); the viewport and the
headless pictures draw each body of a multi-body design, such as the
cells of a partitioned part, in its own colour from the theme (eight in
turn), and a single body in the geometry colour as before.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

crates/ui-egui/src/scene.rs

@@ -79,7 +79,11 @@ pub fn build(display: &DisplayMesh, style: Style, show: Show, t: &Tokens) -> Sce
             s.tris = display.tris.iter().map(|d| SceneTri { p: d.p, normal: d.normal, color: rgb(t.element(d.kind)) }).collect();
         }
         if !mesh_faces && show.geometry {
-            s.tris.extend(display.surface_tris.iter().map(|d| SceneTri { p: d.p, normal: d.normal, color: rgb(t.geometry) }));
+            s.tris.extend(display.surface_tris.iter().map(|d| SceneTri {
+                p: d.p,
+                normal: d.normal,
+                color: rgb(display.body_color(d, t.geometry, &t.bodies)),
+            }));
         }
     }
     if style != Style::Shaded && show.mesh {