In the App Programming Guide for iOS:
Remove sensitive information from views before moving to the background.
When an app transitions to the background, the system takes a snapshot of the app’s main window, which it then presents briefly when transitioning your app back to the foreground.
As I was struggling with this more than once, and the web isn't really clear on what to do, I decided to take what's out there, adding some of my own in order to explain how to create subplots which have one colorbar and they are scaled according to it.
I have tested this using latest Matlab but I'm pretty sure it'll work in older versions.