enhancement: boxes: Re Stream marker colors rendered.

Style improvements:
 * Stream prefixes' color rendered.
 * The topic prefix is not rendered to make equivalence with the webapp.

Tests updated and added (marker/color rendering).

Partially fixes #783.

Author: Ezio-Sarthak

tests/ui_tools/test_boxes.py

@@ -315,10 +315,14 @@ def test__stream_box_autocomplete(self, mocker, write_box, text, state,
                                                     matching_streams)
 
     @pytest.mark.parametrize([
-        'stream_name', 'stream_id', 'expected_marker', 'is_valid_stream'], [
-      ('Secret stream', 99, STREAM_MARKER_PRIVATE, True),
-      ('Stream 1',       1, STREAM_MARKER_PUBLIC,  True),
-      ('Stream 0',       0, STREAM_MARKER_INVALID, False),
+        'stream_name',
+        'stream_id',
+        'expected_marker',
+        'is_valid_stream',
+        'expected_color'], [
+      ('Secret stream', 99, STREAM_MARKER_PRIVATE, True,  '#ccc'),
+      ('Stream 1',       1, STREAM_MARKER_PUBLIC,  True,  '#b0a5fd'),
+      ('Stream 0',       0, STREAM_MARKER_INVALID, False, 'general_bar'),
      ], ids=[
         'private_stream',
         'public_stream',
@@ -327,7 +331,7 @@ def test__stream_box_autocomplete(self, mocker, write_box, text, state,
     def test__set_stream_write_box_style_markers(self, write_box, stream_id,
                                                  stream_name, is_valid_stream,
                                                  expected_marker, stream_dict,
-                                                 mocker):
+                                                 mocker, expected_color):
         # FIXME: Needs refactoring?
         write_box.model.stream_dict = stream_dict
         write_box.stream_id = stream_id
@@ -337,6 +341,7 @@ def test__set_stream_write_box_style_markers(self, write_box, stream_id,
         write_box._set_stream_write_box_style(write_box, stream_name)
 
         assert write_box.header_write_box[0].text == expected_marker
+        assert expected_color in str(write_box.header_write_box[0].get_text())
 
     @pytest.mark.parametrize('text, expected_text', [
         ('Som', 'Some general stream'),

zulipterminal/ui_tools/boxes.py

@@ -142,14 +142,17 @@ def _set_stream_write_box_style(self, widget: ReadlineEdit,
                                     new_text: str) -> None:
         # FIXME: Needs refactoring?
         stream_marker = STREAM_MARKER_INVALID
+        color = 'general_bar'
         if self.model.is_valid_stream(new_text):
             stream = self.model.stream_dict[
                      self.model.stream_id_from_name(new_text)]
             if stream['invite_only']:
                 stream_marker = STREAM_MARKER_PRIVATE
             else:
                 stream_marker = STREAM_MARKER_PUBLIC
+            color = stream['color']
         self.header_write_box[0].set_text(stream_marker)
+        self.header_write_box[0].set_text((color, stream_marker))
 
     def _topic_box_autocomplete(self, text: str, state: Optional[int]
                                 ) -> Optional[str]: