Fix bug with already used colors being used first for new tx labels (#2077)

* Extend list of available tx label colors

* Ensure unknown label colors are given the least priority

closes #2072

* Remove new label colors

BTCPayServer/Controllers/WalletsController.cs

@@ -115,7 +115,7 @@ namespace BTCPayServer.Controllers
             "#ff7619",
             "#84b6eb",
             "#5319e7",
-            "#000000",
+            "#cdcdcd",
             "#cc317c",
         };
 
@@ -173,7 +173,12 @@ namespace BTCPayServer.Controllers
                         allColors
                         .GroupBy(k => k)
                         .OrderBy(k => k.Count())
-                        .ThenBy(k => Array.IndexOf(LabelColorScheme, k.Key))
+                        .ThenBy(k => {
+                            var indexInColorScheme = Array.IndexOf(LabelColorScheme, k.Key);
+
+                            // Ensures that any label color which may not be in our label color scheme is given the least priority
+                            return indexInColorScheme == -1 ? double.PositiveInfinity : indexInColorScheme;
+                        })
                         .First().Key;
                     walletBlobInfo.LabelColors.Add(addlabel, chosenColor);
                     await WalletRepository.SetWalletInfo(walletId, walletBlobInfo);