Start to improve messages appearance

lib/ui/widgets/conversation_file_tile.dart

@@ -13,11 +13,9 @@ import 'package:url_launcher/url_launcher.dart';
 class ConversationFileWidget extends StatefulWidget {
   final int messageID;
   final ConversationMessageFile file;
-  final Color defaultBackgroundColor;
 
   const ConversationFileWidget({
     Key key,
-    @required this.defaultBackgroundColor,
     @required this.messageID,
     @required this.file,
   })  : assert(messageID != null),
@@ -53,7 +51,6 @@ class _ConversationFileWidgetState extends State<ConversationFileWidget> {
       // We open it in the browser
       default:
         return Container(
-          color: widget.defaultBackgroundColor,
           child: Center(
             child: MaterialButton(
               child: Column(