Why does the address book turn black?

Because dark mode is turned on, the address book will turn black.

Dark mode is an interface display setting used on mobile phones, which changes the background color to black or dark to reduce the irritation to eyes and provide a better reading experience. When you turn on the dark mode, the system will automatically adjust the interface color of the application to adapt to the dark background. Therefore, when you turn on the dark mode, the background color of the address book will also become a black background. This is a personalized setting, which can be adjusted according to personal preference.