Change some label colors (#9051)

* Change label colors

* Override black basic label background for green theme on label list

web_src/less/themes/arc-green.less

@@ -1074,6 +1074,10 @@ input {
     color: #87ab63 !important;
 }
 
+.repository.labels .ui.basic.black.label {
+    background-color: #bbbbbb !important;
+}
+
 .lines-commit {
     background: #2e323e !important;
 }