Why are all my iPhone apps pink?

Please review the information in the Apple Support article I linked to below, to learn how to reset your colors.

Customize apps and widgets on the iPhone Home Screen - Apple Support

Go to the Home Screen.Touch and hold the Home Screen background until the icons begin to jiggle. Tap Edit at the top of the screen, then choose Customize and then Tinted, where you can change the tint of the icons.