Clarify default black background in nick-colors

README.rst

@@ -125,6 +125,7 @@ TODO
   * Match ``[nick-colors]]`` by feed URLs using the ``[following]`` mapping
     internally, but still keep nicks as keys.
 
+* Support nicer colors.
 * Ability to show the txt's raw text.
 * Manage subscriptions.
 * Reload feeds.
@@ -340,6 +341,7 @@ selected.
 In this section you can customize how certain mentions and twt authors should
 be rendered. Those settings map a nick to a fore- and background color. In
 contrast to the ``[colors]`` section above, the background here is optional.
+It defaults to ``black`` when omitted.
 When focusing a twt, the fore- and backgorund colors are swapped. There is no
 separate mechanism to come up with a completely different color schemes for
 normal and focus states.