How to increase contrast in iOS 12 for iPhone/iPad/iPod Touch

This feature can be used in combination with other accessibility settings such as ‘Bold Text’, ‘Colour Filters’ and ‘Invert Colours’.

1. Open the ‘Accessibility Settings’: Settings > General > Accessibility. (See the article Open Accessibility Preferences on this website for more information.)
2. Under the ‘Vision’ section, tap ‘Increase Contrast.
   
3. Tap the on/off toggle switch next to 'Increase Contrast'.
   
4. When you are happy with your settings, either tap the back button in the top left of the screen to return to the main ‘Accessibility’ settings screen or press your device’s ‘Home’ button to return to the home screen.

More information:

How to enable 'Bold' text

How to enable 'Colour Filers'

How to enable 'Invert Colours'