title: How to calculate the time in background and make SKAction jump to the time after
body: <p>I am working on an app based on sprite kit. I know that all actions will be paused while the app is in background. However, I am doing the fading color thing so I want to calculate the time while the app is in background and make the SKAction which is the fading action jump the time after so that it doesn't look like the color is not changing while the app is in background. So can someone give me some detailed walkthrough about how to do so? Thanks so much!!</p>