wip nfc make text color static

Author: gnprice

lib/widgets/message_list.dart

@@ -474,13 +474,13 @@ class DateSeparator extends StatelessWidget {
 
   final Message message;
 
+  // This color matches recipient headers.  TODO is that what we want?
+  static final _textColor = Colors.black.withOpacity(0.4);
+
   @override
   Widget build(BuildContext context) {
     final zulipLocalizations = ZulipLocalizations.of(context);
 
-    // This color matches recipient headers.  TODO is that what we want?
-    final color = Colors.black.withOpacity(0.4);
-
     return ColoredBox(color: Colors.white,
       child: Padding(
         padding: const EdgeInsets.symmetric(vertical: 8, horizontal: 2),
@@ -497,7 +497,7 @@ class DateSeparator extends StatelessWidget {
             // TODO dedupe with RecipientHeaderDate
             child: Text(
               style: TextStyle(
-                color: color,
+                color: _textColor,
                 fontFamily: 'Source Sans 3',
                 fontSize: 16,
                 // In Figma this has a line-height of 19, but using 18