Load articles from storage when they are available instead of web.

Test Plan:
- Make sure logged message indicates it was loaded from storage for
  downloaded articles.
- Make sure logged message indicates itw as loaded from web for non
  downloaded articles
Use default color when none is available for new domains

There was a new college admissions section added.  And it had no color
on the main page for the left color-block.  This makes it have a default
color.

Test Plan:
- Make sure college admissions uses the new color
Make sure topic headers have default color, but use black as the default
for other things like settings, downloads, root, ...

Test Plan:
- Look at the different headers and make sure they appear in the correct
  color.