After updating ios15.4.1 my iphone 12 screen turns to pink whenever I

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Restart your iPhone - Apple Support and try again.

If the issue persists, see: If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open - Apple Support.

If you need more help, contact Apple: Get Support.

Jack

Probably you have turned on Night Shift

• Open Control Center. Firmly press the Brightness control icon, then tap to turn Night Shift on or off.
• Go to Settings > Display & Brightness > Night Shift. 2 On the same screen, you can schedule a time for Night Shift to turn on automatically and adjust color temperature.

Use Night Shift on your iPhone, iPad, and iPod touch - Apple ...