diff --git a/src/TeamsISO.App/Assets/_recolor_dragon.py b/src/TeamsISO.App/Assets/_recolor_dragon.py
new file mode 100644
index 0000000..2ce5caf
--- /dev/null
+++ b/src/TeamsISO.App/Assets/_recolor_dragon.py
@@ -0,0 +1,34 @@
+from PIL import Image
+import os
+
+# We treat the navy-blue dragon-mark.png as a silhouette source: anything with
+# nontrivial alpha is "dragon", everything else stays transparent. We emit a
+# pure-black and pure-white variant, tightly cropped to the actual content
+# bbox so they center cleanly when used as a watermark.
+ROOT = os.path.dirname(os.path.abspath(__file__))
+src_path = os.path.join(ROOT, "dragon-mark.png")
+src = Image.open(src_path).convert("RGBA")
+
+alpha = src.split()[-1]
+# Threshold to drop anti-alias fringe that can fool getbbox into reporting
+# the whole canvas as "in".
+mask = alpha.point(lambda v: 255 if v > 16 else 0)
+bbox = mask.getbbox()
+print("content bbox =", bbox, "size =", (bbox[2] - bbox[0], bbox[3] - bbox[1]))
+
+cropped = src.crop(bbox)
+_, _, _, ca = cropped.split()
+
+for name, rgb in (("black", (0, 0, 0)), ("white", (255, 255, 255))):
+    flat = Image.merge(
+        "RGBA",
+        (
+            Image.new("L", cropped.size, rgb[0]),
+            Image.new("L", cropped.size, rgb[1]),
+            Image.new("L", cropped.size, rgb[2]),
+            ca,
+        ),
+    )
+    out_path = os.path.join(ROOT, f"dragon-mark-{name}.png")
+    flat.save(out_path, "PNG", optimize=True)
+    print("wrote", out_path, flat.size)
diff --git a/src/TeamsISO.App/Assets/dragon-mark-black.png b/src/TeamsISO.App/Assets/dragon-mark-black.png
new file mode 100644
index 0000000..c856193
Binary files /dev/null and b/src/TeamsISO.App/Assets/dragon-mark-black.png differ
diff --git a/src/TeamsISO.App/Assets/dragon-mark-white.png b/src/TeamsISO.App/Assets/dragon-mark-white.png
new file mode 100644
index 0000000..f374b81
Binary files /dev/null and b/src/TeamsISO.App/Assets/dragon-mark-white.png differ
diff --git a/src/TeamsISO.App/MainWindow.xaml b/src/TeamsISO.App/MainWindow.xaml
index 594dc87..a23a5ff 100644
--- a/src/TeamsISO.App/MainWindow.xaml
+++ b/src/TeamsISO.App/MainWindow.xaml
@@ -106,7 +106,11 @@
                             BorderThickness="0"
                             Cursor="Hand"
                             ToolTip="About TeamsISO">
-                        <Image Source="/Assets/dragon-mark.png"
+                        <!-- Source bound to Wd.BrandMark.Image so the mark flips
+                             white↔black with the active theme (see Theme.Dark /
+                             Theme.Light). The PNG carries its own AA so HighQuality
+                             scaling is preferred over NearestNeighbor at this size. -->
+                        <Image Source="{DynamicResource Wd.BrandMark.Image}"
                                Width="20" Height="20"
                                RenderOptions.BitmapScalingMode="HighQuality"/>
                     </Button>
@@ -447,8 +451,30 @@
                     BorderBrush="{DynamicResource Wd.Border}"
                     BorderThickness="1"
                     CornerRadius="{StaticResource Radius.M}"
-                    Background="{DynamicResource Wd.Surface}">
+                    Background="{DynamicResource Wd.Surface}"
+                    ClipToBounds="True">
                 <Grid>
+                <!--
+                    Brand watermark superimposed BEHIND the participants grid.
+                    Sits at 6% opacity so a populated grid reads cleanly over
+                    the top while the dragon is still visible through the
+                    transparent row backgrounds (RowBackground="Transparent"
+                    on the DataGrid below). When the grid is empty the
+                    watermark becomes the de-facto empty-state surface.
+
+                    IsHitTestVisible=False so the watermark never absorbs
+                    clicks meant for grid rows or the empty area below them.
+                    Source binds to the theme-flipped Wd.BrandMark.Image
+                    resource — white dragon in dark mode, black in light.
+                -->
+                <Image Source="{DynamicResource Wd.BrandMark.Image}"
+                       Opacity="0.06"
+                       Stretch="Uniform"
+                       HorizontalAlignment="Center"
+                       VerticalAlignment="Center"
+                       Margin="40"
+                       IsHitTestVisible="False"
+                       RenderOptions.BitmapScalingMode="HighQuality"/>
                 <DataGrid x:Name="ParticipantsGrid"
                           ItemsSource="{Binding ParticipantsView}"
                           AutoGenerateColumns="False"
diff --git a/src/TeamsISO.App/TeamsISO.App.csproj b/src/TeamsISO.App/TeamsISO.App.csproj
index eda516d..90cb57d 100644
--- a/src/TeamsISO.App/TeamsISO.App.csproj
+++ b/src/TeamsISO.App/TeamsISO.App.csproj
@@ -60,7 +60,17 @@
 
   <!-- Wild Dragon brand assets — embedded as resources so the published binary is self-contained. -->
   <ItemGroup>
+    <!-- Source navy-blue dragon-mark, kept for AboutWindow / installer iconography. -->
     <Resource Include="Assets\dragon-mark.png" />
+    <!--
+      Theme-aware silhouette variants used by Theme.Dark / Theme.Light to expose
+      a single Wd.BrandMark.Image resource key. The dark theme picks the white
+      dragon (visible on #0A0A0A), the light theme picks the black dragon
+      (visible on #FAFAFB). Generated from dragon-mark.png via
+      Assets/_recolor_dragon.py — re-run if the source mark ever changes.
+    -->
+    <Resource Include="Assets\dragon-mark-white.png" />
+    <Resource Include="Assets\dragon-mark-black.png" />
     <Resource Include="Assets\wild-dragon-wordmark.png" />
     <Resource Include="Assets\teamsiso.ico" />
     <!--
diff --git a/src/TeamsISO.App/Themes/Theme.Dark.xaml b/src/TeamsISO.App/Themes/Theme.Dark.xaml
index 8bad20b..2a748b2 100644
--- a/src/TeamsISO.App/Themes/Theme.Dark.xaml
+++ b/src/TeamsISO.App/Themes/Theme.Dark.xaml
@@ -44,4 +44,20 @@
     <SolidColorBrush x:Key="Wd.Status.LiveBg"    Color="#13261A"/>
     <SolidColorBrush x:Key="Wd.Status.Warn"      Color="#FBBF24"/>
     <SolidColorBrush x:Key="Wd.Status.Error"     Color="#FB819C"/>
+
+    <!--
+        Brand mark image, theme-flipped. Dark mode shows the WHITE dragon so it
+        reads against the near-black canvas. The light theme exposes the same
+        key pointing at the BLACK dragon. Consumers bind via
+        {DynamicResource Wd.BrandMark.Image} so the swap is automatic on
+        ThemeManager.Toggle().
+
+        CacheOption=OnLoad decodes the PNG at load time and releases the
+        underlying stream, which matters because the source files are 1243×1125
+        — without OnLoad the BitmapImage holds the stream open for the life
+        of the resource dictionary.
+    -->
+    <BitmapImage x:Key="Wd.BrandMark.Image"
+                 UriSource="pack://application:,,,/TeamsISO;component/Assets/dragon-mark-white.png"
+                 CacheOption="OnLoad"/>
 </ResourceDictionary>
diff --git a/src/TeamsISO.App/Themes/Theme.Light.xaml b/src/TeamsISO.App/Themes/Theme.Light.xaml
index f1e64bc..90c774b 100644
--- a/src/TeamsISO.App/Themes/Theme.Light.xaml
+++ b/src/TeamsISO.App/Themes/Theme.Light.xaml
@@ -46,4 +46,15 @@
     <SolidColorBrush x:Key="Wd.Status.LiveBg"    Color="#DCFCE7"/>
     <SolidColorBrush x:Key="Wd.Status.Warn"      Color="#B45309"/>
     <SolidColorBrush x:Key="Wd.Status.Error"     Color="#D43E5C"/>
+
+    <!--
+        Brand mark image, theme-flipped. Light mode shows the BLACK dragon so it
+        reads against the cyan-tinted off-white canvas. Mirror of the Dark
+        theme's resource — same key, opposite silhouette. Consumers use
+        {DynamicResource Wd.BrandMark.Image} so the swap is automatic.
+        See Theme.Dark.xaml's comment for the CacheOption=OnLoad rationale.
+    -->
+    <BitmapImage x:Key="Wd.BrandMark.Image"
+                 UriSource="pack://application:,,,/TeamsISO;component/Assets/dragon-mark-black.png"
+                 CacheOption="OnLoad"/>
 </ResourceDictionary>