The iPhone has an easy-to-understand user interface so that anyone can understand how to use it without a manual, but elaborate use is also possible if you are interested. If you can use the iPhone on a monochrome screen … it is said that if it is grayscale (256 gradations) instead of monochrome (2 gradations), anyone can use it in a simple way regardless of whether it feels shibbish You can.
To change the screen to grayscale, use the iPhone's "zoom function". The zoom function is a display mode that makes it easier to see characters and images by enlarging a part or the whole of the screen. Double-tap the screen with three fingers to enable / disable it. You can change the function on / off and enlargement ratio by opening the screen in the order of "Settings" → "Accessibility" → "Zoom function".
To display the screen in grayscale, use the filters available when the zoom function is enabled. Triple-tap the screen with three fingers to call the setting panel of the zoom function, and tap "Select Filter". If you select "Grayscale" from the options that appear, the subsequent screen will be grayscale.
In addition to applying the filter of the zoom function to the entire screen, it can be applied only to a part of the screen (for a rectangular area like a window). The whole screen can be used in full color and grayscale only partially, so you can use it freely according to your preference. Full color may be just right for those who have a flickering eye.