How to set the contrast color of Apple's mobile phone 7 camera?

First open the "camera" icon on the iPhone 7 desktop, as shown in the figure below.

2. After entering the camera interface, click the option in the red box at the top of the page below, as shown in the figure below.

Third, then turn on the flash function of the mobile phone, as shown in the figure below.

Fourth, finally, find the "Contrast Color" item in the camera settings and click it to set the camera contrast color.