Change unlock screen appearance
Solution 1:
There's currently no way to configure the appearance of the lock screen.
However, there is work in progress to improve the appearance of the lock screen by replacing it with the same software that powers the login screen.
Completion of that work is contingent upon development for the next version of Unity and the Mir project, which is planned to drastically revamp the underlying systems behind the login screen, graphical login sessions, user switching, and the lock screen.
A preliminary version of the next version of Unity with an improved lock screen is scheduled to be available for use by developers next month, and the finished product with Mir is planned to be included in Ubuntu 14.04.