Improve docs for colors (#6473)

packages/flutter/lib/src/material/icon.dart

@@ -12,13 +12,15 @@ import 'theme.dart';
 
 /// A material design icon.
 ///
-/// Available icons are shown on this page:
-/// <https://design.google.com/icons/>
+/// Icons are not interactive. For an interactive icon, consider [IconButton].
 ///
 /// Icons are identified by their name (as given on that page), with
 /// spaces converted to underscores, from the [Icons] class. For
 /// example, the "alarm add" icon is [Icons.alarm_add].
 ///
+/// Available icons are shown on this page:
+/// <https://design.google.com/icons/>
+///
 /// To use this class, make sure you set `uses-material-design: true`
 /// in your project's `flutter.yaml` file. This ensures that the
 /// MaterialIcons font is included in your application. This font is