Custom backgrounds: Do not print the default background color when it has been saved to the DB.

props obenland.
fixes #22030.


git-svn-id: https://develop.svn.wordpress.org/trunk@27703 602fd350-edb4-49c9-b593-d223f7449a82
Custom backgrounds: Always cause a preview in the customizer.

Omitted from [27703].

props obenland.
see #22030.


git-svn-id: https://develop.svn.wordpress.org/trunk@27704 602fd350-edb4-49c9-b593-d223f7449a82