Reduce White Point feature reduces the intensity of bright colors.
By default, it is not enabled on your iPhone.
If you want to enable it, here are the steps (here, I’m using iPhone X (iOS 13.3)):
Hit Accessibility which you can find between Display & Brightness and Wallpaper.
Tap Display & Text Size which you can find between Magnifier and Motion.
Scroll down to the bottom. Hit the toggle switch beside Reduce White Point, which you can find above Auto-Brightness.
Now you can see a slider beneath Reduce White Point. Slide it to the right (to decrease the intensity of bright colors) or left (to increase the intensity of bright colors).
Note: follow the above steps (1-4) to disable the Reduce White Point feature.