Color blind mode
For people with color blindness, iOS and Android offer an option to better see the difference between colors. This setting can also be used by people who, for example, find a yellower screen light more pleasant to read on their tablet or telephone.
On iOS, this accessibility feature is called Color Filters. It is possible to choose shades of gray or other filters that can also be set in intensity.
On Android, adjusting the colors on the screen is called Color Correction. Android offers fewer color filters than iOS. It is, however, possible to pin a shortcut for color correction on the screen.
The metric for color blind mode is not available on iOS at the moment.
More about color blind modeuse color blind mode on Android.
Incidentally, both iOS and Android also offer the option to completely invert colors.