Property panel: display and edit primvars:displayColor[] as color swatches

DrawVtValueWidget now handles Color-role array attributes (VtArray<GfVec3f>
and VtArray<GfVec4f>) that previously fell through to the generic [array N]
fallback.

- Single element: inline ColorEdit3/4
- Multiple elements: collapsible row with up to 5 swatch previews + [N] count;
  expanded view shows per-index ColorEdit3/4 (capped at 16 entries)
- Editing any element writes the full modified VtArray back via attr.Set()

Covers primvars:displayColor, primvars:displayOpacity[], and any other
color3f[]/color4f[] primvar.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ui/PropertyPanel.cpp

@@ -577,8 +577,9 @@ static pxr::VtValue DrawVtValueWidget(pxr::UsdAttribute& attr,
 {
     using namespace pxr;
 
-    // Color role → ColorEdit3/4
+    // Color role → ColorEdit3/4 (scalar and array)
     if (attr.GetRoleName() == TfToken("Color")) {
+        // ---- scalar ----
         if (val.IsHolding<GfVec3f>()) {
             GfVec3f c = val.UncheckedGet<GfVec3f>();
             if (ImGui::ColorEdit3("##col", c.data()))
@@ -591,6 +592,99 @@ static pxr::VtValue DrawVtValueWidget(pxr::UsdAttribute& attr,
                 return VtValue(c);
             return VtValue();
         }
+
+        // ---- color3f[] (e.g. primvars:displayColor) ----
+        if (val.IsHolding<VtArray<GfVec3f>>()) {
+            VtArray<GfVec3f> arr = val.UncheckedGet<VtArray<GfVec3f>>();
+            bool changed = false;
+            if (arr.size() == 1) {
+                GfVec3f c = arr[0];
+                if (ImGui::ColorEdit3("##dc", c.data()))
+                    { arr[0] = c; changed = true; }
+            } else if (!arr.empty()) {
+                // Collapsible: arrow + swatch preview on header line
+                bool open = ImGui::TreeNodeEx("##dcarr",
+                    ImGuiTreeNodeFlags_AllowOverlap | ImGuiTreeNodeFlags_SpanAvailWidth);
+                ImGui::SameLine(0, 6);
+                float sz = ImGui::GetTextLineHeight();
+                size_t shown = std::min(arr.size(), (size_t)5);
+                for (size_t i = 0; i < shown; ++i) {
+                    if (i > 0) ImGui::SameLine(0, 2);
+                    char sid[16]; snprintf(sid, sizeof(sid), "##sv%d", (int)i);
+                    ImGui::ColorButton(sid,
+                        ImVec4(arr[i][0], arr[i][1], arr[i][2], 1.f),
+                        ImGuiColorEditFlags_NoPicker | ImGuiColorEditFlags_NoTooltip,
+                        ImVec2(sz, sz));
+                }
+                ImGui::SameLine(0, 4);
+                ImGui::TextDisabled("[%zu]", arr.size());
+                if (open) {
+                    static constexpr size_t kEditLimit = 16;
+                    size_t lim = std::min(arr.size(), kEditLimit);
+                    for (size_t i = 0; i < lim; ++i) {
+                        ImGui::PushID((int)i);
+                        ImGui::Text("[%d]", (int)i);
+                        ImGui::SameLine();
+                        GfVec3f c = arr[i];
+                        ImGui::SetNextItemWidth(-FLT_MIN);
+                        if (ImGui::ColorEdit3("##ce", c.data()))
+                            { arr[i] = c; changed = true; }
+                        ImGui::PopID();
+                    }
+                    if (arr.size() > kEditLimit)
+                        ImGui::TextDisabled("  ... %zu more", arr.size() - kEditLimit);
+                    ImGui::TreePop();
+                }
+            }
+            if (changed) return VtValue(arr);
+            return VtValue();
+        }
+
+        // ---- color4f[] ----
+        if (val.IsHolding<VtArray<GfVec4f>>()) {
+            VtArray<GfVec4f> arr = val.UncheckedGet<VtArray<GfVec4f>>();
+            bool changed = false;
+            if (arr.size() == 1) {
+                GfVec4f c = arr[0];
+                if (ImGui::ColorEdit4("##dc4", c.data()))
+                    { arr[0] = c; changed = true; }
+            } else if (!arr.empty()) {
+                bool open = ImGui::TreeNodeEx("##dcarr4",
+                    ImGuiTreeNodeFlags_AllowOverlap | ImGuiTreeNodeFlags_SpanAvailWidth);
+                ImGui::SameLine(0, 6);
+                float sz = ImGui::GetTextLineHeight();
+                size_t shown = std::min(arr.size(), (size_t)5);
+                for (size_t i = 0; i < shown; ++i) {
+                    if (i > 0) ImGui::SameLine(0, 2);
+                    char sid[16]; snprintf(sid, sizeof(sid), "##sv4%d", (int)i);
+                    ImGui::ColorButton(sid,
+                        ImVec4(arr[i][0], arr[i][1], arr[i][2], arr[i][3]),
+                        ImGuiColorEditFlags_NoPicker | ImGuiColorEditFlags_NoTooltip,
+                        ImVec2(sz, sz));
+                }
+                ImGui::SameLine(0, 4);
+                ImGui::TextDisabled("[%zu]", arr.size());
+                if (open) {
+                    static constexpr size_t kEditLimit = 16;
+                    size_t lim = std::min(arr.size(), kEditLimit);
+                    for (size_t i = 0; i < lim; ++i) {
+                        ImGui::PushID((int)i);
+                        ImGui::Text("[%d]", (int)i);
+                        ImGui::SameLine();
+                        GfVec4f c = arr[i];
+                        ImGui::SetNextItemWidth(-FLT_MIN);
+                        if (ImGui::ColorEdit4("##ce4", c.data()))
+                            { arr[i] = c; changed = true; }
+                        ImGui::PopID();
+                    }
+                    if (arr.size() > kEditLimit)
+                        ImGui::TextDisabled("  ... %zu more", arr.size() - kEditLimit);
+                    ImGui::TreePop();
+                }
+            }
+            if (changed) return VtValue(arr);
+            return VtValue();
+        }
     }
 
     // ---- Scalar types ----