Changing app names from white to black iphone 13

Greetings vincenza274,

If you are trying to enable Dark Mode on your iPhone, follow the guidance found here:

Use Dark Mode on your iPhone and iPad

"Turn on Dark Mode in Settings or Control Center

1. Go to Settings, then tap Display & Brightness.
2. Select Dark to turn on Dark Mode.

To turn Dark Mode on and off in Control Center:

1. Go to Settings, then tap Control Center.
2. Tap the Add button next to Dark Mode to add it to Control Center.

Learn how to use Control Center on your iPhone or iPad."

If you are having a different issue, provide some more specific detail.

Take care.