diff --git a/Signal/src/ViewControllers/AppSettings/AdvancedSettingsTableViewController.m b/Signal/src/ViewControllers/AppSettings/AdvancedSettingsTableViewController.m
index 1b6ad314b..d6482e6f1 100644
--- a/Signal/src/ViewControllers/AppSettings/AdvancedSettingsTableViewController.m
+++ b/Signal/src/ViewControllers/AppSettings/AdvancedSettingsTableViewController.m
@@ -195,6 +195,16 @@ NS_ASSUME_NONNULL_BEGIN
     }
     [contents addSection:censorshipSection];
 
+#ifdef DEBUG
+    OWSTableSection *themeSection = [OWSTableSection new];
+    themeSection.headerTitle = NSLocalizedString(@"THEME_SECTION", nil);
+    [themeSection addItem:[OWSTableItem switchItemWithText:NSLocalizedString(@"SETTINGS_ADVANCED_THEME", @"")
+                                                      isOn:[Environment.preferences isThemeEnabled]
+                                                    target:weakSelf
+                                                  selector:@selector(didToggleThemeSwitch:)]];
+    [contents addSection:themeSection];
+#endif
+
     self.contents = contents;
 }
 
@@ -274,6 +284,13 @@ NS_ASSUME_NONNULL_BEGIN
     [self updateTableContents];
 }
 
+- (void)didToggleThemeSwitch:(UISwitch *)sender
+{
+    [Environment.preferences setIsThemeEnabled:sender.isOn];
+
+    // TODO: Notify and refresh.
+}
+
 @end
 
 NS_ASSUME_NONNULL_END
diff --git a/Signal/translations/en.lproj/Localizable.strings b/Signal/translations/en.lproj/Localizable.strings
index d852ebce1..ea18bfff8 100644
--- a/Signal/translations/en.lproj/Localizable.strings
+++ b/Signal/translations/en.lproj/Localizable.strings
@@ -1886,6 +1886,9 @@
 /* No comment provided by engineer. */
 "SETTINGS_ADVANCED_SUBMIT_DEBUGLOG" = "Submit Debug Log";
 
+/* No comment provided by engineer. */
+"SETTINGS_ADVANCED_THEME" = "Theme";
+
 /* No comment provided by engineer. */
 "SETTINGS_ADVANCED_TITLE" = "Advanced";
 
@@ -2132,6 +2135,9 @@
 /* Label for button to verify a user's safety number. */
 "SYSTEM_MESSAGE_ACTION_VERIFY_SAFETY_NUMBER" = "Verify Safety Number";
 
+/* No comment provided by engineer. */
+"THEME_SECTION" = "THEME_SECTION";
+
 /* {{number of days}} embedded in strings, e.g. 'Alice updated disappearing messages expiration to {{5 days}}'. See other *_TIME_AMOUNT strings */
 "TIME_AMOUNT_DAYS" = "%@ days";
 
diff --git a/SignalMessaging/utils/OWSPreferences.h b/SignalMessaging/utils/OWSPreferences.h
index fca6588f2..fcd9020da 100644
--- a/SignalMessaging/utils/OWSPreferences.h
+++ b/SignalMessaging/utils/OWSPreferences.h
@@ -61,7 +61,8 @@ extern NSString *const OWSPreferencesCallLoggingDidChangeNotification;
 - (BOOL)hasGeneratedThumbnails;
 - (void)setHasGeneratedThumbnails:(BOOL)value;
 
-#pragma mark - Calling
+- (BOOL)isThemeEnabled;
+- (void)setIsThemeEnabled:(BOOL)flag;
 
 #pragma mark Callkit
 
diff --git a/SignalMessaging/utils/OWSPreferences.m b/SignalMessaging/utils/OWSPreferences.m
index b9ef59659..239d76647 100644
--- a/SignalMessaging/utils/OWSPreferences.m
+++ b/SignalMessaging/utils/OWSPreferences.m
@@ -31,6 +31,7 @@ NSString *const OWSPreferencesKeyHasGeneratedThumbnails = @"OWSPreferencesKeyHas
 NSString *const OWSPreferencesKeyIOSUpgradeNagDate = @"iOSUpgradeNagDate";
 NSString *const OWSPreferencesKey_IsReadyForAppExtensions = @"isReadyForAppExtensions_5";
 NSString *const OWSPreferencesKeySystemCallLogEnabled = @"OWSPreferencesKeySystemCallLogEnabled";
+NSString *const OWSPreferencesKeyEnableTheme = @"OWSPreferencesKeyEnableTheme";
 
 @implementation OWSPreferences
 
@@ -58,7 +59,7 @@ NSString *const OWSPreferencesKeySystemCallLogEnabled = @"OWSPreferencesKeySyste
     OWSAssert(key != nil);
 
     __block id result;
-    [OWSPrimaryStorage.dbReadConnection readWithBlock:^(YapDatabaseReadTransaction *_Nonnull transaction) {
+    [OWSPrimaryStorage.dbReadConnection readWithBlock:^(YapDatabaseReadTransaction *transaction) {
         result = [self tryGetValueForKey:key transaction:transaction];
     }];
     return result;
@@ -72,10 +73,9 @@ NSString *const OWSPreferencesKeySystemCallLogEnabled = @"OWSPreferencesKeySyste
 
 - (void)setValueForKey:(NSString *)key toValue:(nullable id)value
 {
-    [OWSPrimaryStorage.dbReadWriteConnection
-        readWriteWithBlock:^(YapDatabaseReadWriteTransaction *_Nonnull transaction) {
-            [self setValueForKey:key toValue:value transaction:transaction];
-        }];
+    [OWSPrimaryStorage.dbReadWriteConnection readWriteWithBlock:^(YapDatabaseReadWriteTransaction *transaction) {
+        [self setValueForKey:key toValue:value transaction:transaction];
+    }];
 }
 
 - (void)setValueForKey:(NSString *)key
@@ -414,6 +414,19 @@ NSString *const OWSPreferencesKeySystemCallLogEnabled = @"OWSPreferencesKeySyste
     }
 }
 
+- (BOOL)isThemeEnabled
+{
+    NSNumber *preference = [self tryGetValueForKey:OWSPreferencesKeyEnableTheme];
+    return preference ? [preference boolValue] : NO;
+}
+
+- (void)setIsThemeEnabled:(BOOL)flag
+{
+    OWSAssert(CurrentAppContext().isMainApp);
+
+    [self setValueForKey:OWSPreferencesKeyEnableTheme toValue:@(flag)];
+}
+
 #pragma mark - Push Tokens
 
 - (void)setPushToken:(NSString *)value