Changing section colors does not rebuild things
I want to use section colors in all post headers, and I have to run `nikola build -a` to get the changes to appear everywhere.

diff --git a/nikola/nikola.py b/nikola/nikola.py
index e3b2ed3b9..a961d2525 100644
--- a/nikola/nikola.py
+++ b/nikola/nikola.py
@@ -441,6 +441,7 @@ class Nikola(object):
             'POSTS': (("posts/*.txt", "posts", "post.tmpl"),),
             'POSTS_SECTIONS': True,
             'POSTS_SECTION_ARE_INDEXES': True,
+            'POSTS_SECTION_COLORS': {},
             'POSTS_SECTION_DESCRIPTIONS': "",
             'POSTS_SECTION_FROM_META': False,
             'POSTS_SECTION_NAME': "",
@@ -945,7 +946,13 @@ class Nikola(object):
         self._GLOBAL_CONTEXT['hidden_categories'] = self.config.get('HIDDEN_CATEGORIES')
         self._GLOBAL_CONTEXT['hidden_authors'] = self.config.get('HIDDEN_AUTHORS')
         self._GLOBAL_CONTEXT['url_replacer'] = self.url_replacer
-        self._GLOBAL_CONTEXT['post_section_colors'] = self.config.get('POST_SECTION_COLORS')
+        self._GLOBAL_CONTEXT['posts_sections'] = self.config.get('POSTS_SECTIONS')
+        self._GLOBAL_CONTEXT['posts_section_are_indexes'] = self.config.get('POSTS_SECTION_ARE_INDEXES')
+        self._GLOBAL_CONTEXT['posts_section_colors'] = self.config.get('POSTS_SECTION_COLORS')
+        self._GLOBAL_CONTEXT['posts_section_descriptions'] = self.config.get('POSTS_SECTION_DESCRIPTIONS')
+        self._GLOBAL_CONTEXT['posts_section_from_meta'] = self.config.get('POSTS_SECTION_FROM_META')
+        self._GLOBAL_CONTEXT['posts_section_name'] = self.config.get('POSTS_SECTION_NAME')
+        self._GLOBAL_CONTEXT['posts_section_title'] = self.config.get('POSTS_SECTION_TITLE')
 
         # IPython theme configuration.  If a website has ipynb enabled in post_pages
         # we should enable the IPython CSS (leaving that up to the theme itself).
['nikola/nikola.py']