Which of the following uses a colon correctly?

The best way to achieve success is to focus: on one thing perseverance.
The best way: to achieve success is to focus on one thing perseverance.
The best way to achieve success is to focus on one thing: perseverance.
The best way to achieve: success is to focus on one thing perseverance.

The best way to achieve success is to focus on one thing: perseverance.