[tmux integration] Store "none" for the tab color when tab color is off for a...

[tmux integration] Store "none" for the tab color when tab color is off for a session. This fixes a bug where new tmux sessions didn't use the profile's color. Uninitialized (which is now indicated as an unset tab color) should (and now does) mean to use the profile's value. "none" means no color. Otherwise it'll be a #hex value.

Issue 6320

sources/PTYSession.m

@@ -196,6 +196,10 @@ static NSString *const kVariableKeySessionCreationTimeString = @"session.creatio
 static NSString *const kVariableKeySessionPID = @"iterm2.pid";
 static NSString *const kVariableKeySessionAutoLogID = @"session.autoLogId";
+// Value for SESSION_ARRANGEMENT_TMUX_TAB_COLOR that means "don't use the
+// default color from the tmux profile; this tab should have no color."
+static NSString *const iTermTmuxTabColorNone = @"none";
+
 // Maps Session GUID to saved contents. Only live between window restoration
 // and the end of startup activities.
 static NSMutableDictionary *gRegisteredSessionContents;
@@ -963,7 +967,8 @@ ITERM_WEAKLY_REFERENCEABLE
     }
     if ([arrangement objectForKey:SESSION_ARRANGEMENT_TMUX_PANE]) {
         // This is a tmux arrangement.
-        NSDictionary *tabColorDict = [ITAddressBookMgr encodeColor:[NSColor colorFromHexString:arrangement[SESSION_ARRANGEMENT_TMUX_TAB_COLOR]]];
+        NSString *colorString = arrangement[SESSION_ARRANGEMENT_TMUX_TAB_COLOR];
+        NSDictionary *tabColorDict = [ITAddressBookMgr encodeColor:[NSColor colorFromHexString:colorString]];
         if (tabColorDict) {
             // We're restoring a tmux arrangement that specifies a tab color.
             if (![iTermProfilePreferences boolForKey:KEY_USE_TAB_COLOR inProfile:theBookmark] ||
@@ -973,7 +978,8 @@ ITERM_WEAKLY_REFERENCEABLE
                 theBookmark = [theBookmark dictionaryBySettingObject:@YES forKey:KEY_USE_TAB_COLOR];
                 needDivorce = YES;
             }
-        } else if ([iTermProfilePreferences boolForKey:KEY_USE_TAB_COLOR inProfile:theBookmark]) {
+        } else if ([colorString isEqualToString:iTermTmuxTabColorNone] &&
+                   [iTermProfilePreferences boolForKey:KEY_USE_TAB_COLOR inProfile:theBookmark]) {
             // There was no tab color but the tmux profile specifies one. Disable it and divorce.
             theBookmark = [theBookmark dictionaryBySettingObject:@NO forKey:KEY_USE_TAB_COLOR];
             needDivorce = YES;
@@ -3444,7 +3450,8 @@ ITERM_WEAKLY_REFERENCEABLE
             tabColorDict = nil;
         }
         NSColor *tabColor = [ITAddressBookMgr decodeColor:tabColorDict];
-        [self.tmuxController setTabColorString:[tabColor hexString] forWindowPane:_tmuxPane];
+        [self.tmuxController setTabColorString:tabColor ? [tabColor hexString] : iTermTmuxTabColorNone
+                                 forWindowPane:_tmuxPane];
     }
 }