Is it possible to create interactive code in Mathematica (via EventHandler[] or Manipulate[] perhaps) that continually updates some calculation based on external data in the time when no user input is received?
As a trivial example, code that shows the current time, with seconds, continually updating, and which allows the user to click on any of the numbers to change their color.
Thank you.

Clockin the documentation. In fact, this question is quite unspecific. For example, do you want the updates to continue when the relevant cell is not being displayed on the screen? Dynamic doesn't permit that. What is it you're trying to achieve? What have you tried? $\endgroup$