Added a grey color for visitors

You don't see visitors without hovering the specific user. So you would have to check everyone by yourself. This highlights them grey. (You're also marked as visitor when you're muted)

css/converse.css

@@ -880,6 +880,8 @@
         white-space: nowrap; }
         #conversejs .chatroom .participant-list li.moderator {
           color: #8f2831; }
+        #conversejs .chatroom .participant-list li.visitor {
+          color: #A3A3A3; }
     #conversejs .chatroom .chat-textarea {
       border-bottom-right-radius: 0; }
     #conversejs .chatroom .chat-area {