diff --git a/packages/browseros/chromium_patches/chrome/browser/browseros/core/browseros_prefs.cc b/packages/browseros/chromium_patches/chrome/browser/browseros/core/browseros_prefs.cc
index 134306e3f..8b377597a 100644
--- a/packages/browseros/chromium_patches/chrome/browser/browseros/core/browseros_prefs.cc
+++ b/packages/browseros/chromium_patches/chrome/browser/browseros/core/browseros_prefs.cc
@@ -1,9 +1,9 @@
 diff --git a/chrome/browser/browseros/core/browseros_prefs.cc b/chrome/browser/browseros/core/browseros_prefs.cc
 new file mode 100644
-index 0000000000000..f37f67aa3aca1
+index 0000000000000..f3a2e43cd7af2
 --- /dev/null
 +++ b/chrome/browser/browseros/core/browseros_prefs.cc
-@@ -0,0 +1,73 @@
+@@ -0,0 +1,90 @@
 +// Copyright 2025 The Chromium Authors
 +// Use of this source code is governed by a BSD-style license that can be
 +// found in the LICENSE file.
@@ -13,6 +13,8 @@ index 0000000000000..f37f67aa3aca1
 +#include "chrome/browser/ui/actions/chrome_action_id.h"
 +#include "chrome/common/pref_names.h"
 +#include "components/pref_registry/pref_registry_syncable.h"
++#include "third_party/skia/include/core/SkColor.h"
++#include "ui/base/mojom/themes.mojom.h"
 +
 +namespace browseros {
 +
@@ -57,6 +59,21 @@ index 0000000000000..f37f67aa3aca1
 +  }
 +}
 +
++void SyncDefaultTheme(PrefService* pref_service) {
++  const PrefService::Preference* user_color_pref =
++      pref_service->FindPreference(::prefs::kUserColor);
++  if (user_color_pref && user_color_pref->IsDefaultValue()) {
++    // Blue tonal spot: SkColorSetRGB(140, 171, 228)
++    pref_service->SetInteger(::prefs::kUserColor,
++                             static_cast<int>(SkColorSetRGB(140, 171, 228)));
++    pref_service->SetString(::prefs::kCurrentThemeID,
++                            "user_color_theme_id");
++    pref_service->SetInteger(
++        ::prefs::kBrowserColorVariant,
++        static_cast<int>(ui::mojom::BrowserColorVariant::kTonalSpot));
++  }
++}
++
 +const char* GetVisibilityPrefForAction(actions::ActionId id) {
 +  switch (id) {
 +    case kActionSidePanelShowThirdPartyLlm:
diff --git a/packages/browseros/chromium_patches/chrome/browser/browseros/core/browseros_prefs.h b/packages/browseros/chromium_patches/chrome/browser/browseros/core/browseros_prefs.h
index 46d028ea0..ccd95707a 100644
--- a/packages/browseros/chromium_patches/chrome/browser/browseros/core/browseros_prefs.h
+++ b/packages/browseros/chromium_patches/chrome/browser/browseros/core/browseros_prefs.h
@@ -1,9 +1,9 @@
 diff --git a/chrome/browser/browseros/core/browseros_prefs.h b/chrome/browser/browseros/core/browseros_prefs.h
 new file mode 100644
-index 0000000000000..88cdbb73caf77
+index 0000000000000..2719852d7d8c6
 --- /dev/null
 +++ b/chrome/browser/browseros/core/browseros_prefs.h
-@@ -0,0 +1,76 @@
+@@ -0,0 +1,80 @@
 +// Copyright 2025 The Chromium Authors
 +// Use of this source code is governed by a BSD-style license that can be
 +// found in the LICENSE file.
@@ -67,6 +67,10 @@ index 0000000000000..88cdbb73caf77
 +// reflects BrowserOS's default.
 +void SyncVerticalTabsPref(PrefService* pref_service);
 +
++// Sets the default BrowserOS theme (blue tonal spot) on first run
++// when the user hasn't customized the theme yet.
++void SyncDefaultTheme(PrefService* pref_service);
++
 +// Check if a toolbar action should be shown based on its visibility pref.
 +// Returns true if:
 +//   - Action has no visibility pref (e.g., Assistant - always visible)
diff --git a/packages/browseros/chromium_patches/chrome/browser/themes/BUILD.gn b/packages/browseros/chromium_patches/chrome/browser/themes/BUILD.gn
new file mode 100644
index 000000000..5844215ed
--- /dev/null
+++ b/packages/browseros/chromium_patches/chrome/browser/themes/BUILD.gn
@@ -0,0 +1,12 @@
+diff --git a/chrome/browser/themes/BUILD.gn b/chrome/browser/themes/BUILD.gn
+index 4924b822aa42e..1fcba3a9c4a6c 100644
+--- a/chrome/browser/themes/BUILD.gn
++++ b/chrome/browser/themes/BUILD.gn
+@@ -33,6 +33,7 @@ source_set("themes") {
+   ]
+   deps = [
+     "//chrome/app/theme:theme_resources",
++    "//chrome/browser/browseros/core:prefs",
+     "//chrome/browser/new_tab_page/chrome_colors",
+     "//chrome/browser/search/background",
+     "//chrome/browser/search/background:constants",
diff --git a/packages/browseros/chromium_patches/chrome/browser/themes/theme_service.cc b/packages/browseros/chromium_patches/chrome/browser/themes/theme_service.cc
new file mode 100644
index 000000000..3a2572605
--- /dev/null
+++ b/packages/browseros/chromium_patches/chrome/browser/themes/theme_service.cc
@@ -0,0 +1,20 @@
+diff --git a/chrome/browser/themes/theme_service.cc b/chrome/browser/themes/theme_service.cc
+index 0589bacba844a..14bc76e5475f0 100644
+--- a/chrome/browser/themes/theme_service.cc
++++ b/chrome/browser/themes/theme_service.cc
+@@ -30,6 +30,7 @@
+ #include "base/task/thread_pool.h"
+ #include "base/trace_event/trace_event.h"
+ #include "build/build_config.h"
++#include "chrome/browser/browseros/core/browseros_prefs.h"
+ #include "chrome/browser/extensions/extension_service.h"
+ #include "chrome/browser/extensions/theme_installed_infobar_delegate.h"
+ #include "chrome/browser/new_tab_page/chrome_colors/chrome_colors_util.h"
+@@ -265,6 +266,7 @@ ThemeService::~ThemeService() = default;
+ void ThemeService::Init() {
+   theme_helper_->DCheckCalledOnValidSequence();
+ 
++  browseros::SyncDefaultTheme(profile_->GetPrefs());
+   InitFromPrefs();
+ 
+   // ThemeObserver should be constructed before calling