Support different colors per completion column.

Now colors.completion.fg may be set to a list to specify a different
color for each completion column. For example:

:set colors.completion.fg [black,blue,white] will use black text for the
first column, blue for the second, and white for the third.

Setting to a single value still works and behaves as before. The default
is unchanged from 'white'.

Resolves #1794.

qutebrowser/completion/completiondelegate.py

@@ -138,10 +138,10 @@ class CompletionItemDelegate(QStyledItemDelegate):
 
         self._painter.translate(text_rect.left(), text_rect.top())
         self._get_textdoc(index)
-        self._draw_textdoc(text_rect)
+        self._draw_textdoc(text_rect, index.column())
         self._painter.restore()
 
-    def _draw_textdoc(self, rect):
+    def _draw_textdoc(self, rect, col):
         """Draw the QTextDocument of an item.
 
         Args:
@@ -156,7 +156,9 @@ class CompletionItemDelegate(QStyledItemDelegate):
         elif not self._opt.state & QStyle.State_Enabled:
             color = config.val.colors.completion.category.fg
         else:
-            color = config.val.colors.completion.fg
+            colors = config.val.colors.completion.fg
+            # if multiple colors are set, use different colors per column
+            color = colors[col % len(colors)]
         self._painter.setPen(color)
 
         ctx = QAbstractTextDocumentLayout.PaintContext()

qutebrowser/config/configdata.yml

@@ -1541,8 +1541,14 @@ zoom.text_only:
 
 colors.completion.fg:
   default: white
-  type: QtColor
+  type:
-  desc: Text color of the completion widget.
+    name: ListOrValue
+    valtype: QtColor
+  desc: >-
+    Text color of the completion widget.
+
+    May be a single value to specify the color for all columns, or a list
+    specifying a different color for each column.
 
 colors.completion.odd.bg:
   default: '#444444'