Further explorations of iOS 10's code may back expectations that the mobile OS will get a "dark mode" in later betas, and/or a cellular connection toggle in its Control Center.
New screenshots show the operating system's hidden "dark mode" working in the Settings app, according to a recent Twitter post by developer Andrew Wiik. That would support speculation that Apple is planning to offer system-wide support, rather than implement app-specific options akin to iBooks.
Wiik was the source of recent screenshots of Messages running in the new mode. Prior to that, various AppleInsider readers noted that asking Siri to turn on dark mode resulted in the assistant saying it's "not able to change that setting," instead of offering a generic response.
Wiik also recently posted a shot of the iOS 10 Simulator with a sixth, blank button near the top of the Control Center. While its purpose is uncertain, Wiik speculated that Apple might be planning a cellular toggle.
iOS 9's Control Center includes options for toggling Wi-Fi, or killing all wireless connections via Airplane Mode, but not a way of just halting cellular data -- something useful when 3G/4G connections are weak or a person is trying to avoid roaming and data cap penalties. At the moment, iOS 9 users have to delve into the Settings app to stop cellular without also affecting Wi-Fi and Bluetooth.
At the moment iOS 10 exists only as a developer beta. A public beta is due in July, followed by an official release in the fall -- most likely in September for new iPhones.