Galaxy S10: All displayed color on screen are only black and white

1. Wind down mode

If you activated Wind down mode, colors on the screen will be shown in black and white tone.

Please check whether this mode is enabled or not by following the below steps :

You can activate Wind down mode to reduce eye strain before sleeping and prevent your sleep from being disturbed.

• Greyscale: Displays colors on the screen as grey tones.
• Do not disturb: Set the device to mute incoming calls and notification sounds, except for allowed exceptions.

2. Night mode

Night mode also can reduce eye strain by applying the dark theme when using the device at night or in a dark place. 

Please check whether night mode is enabled or not by following the given steps : Settings > Display > Night mode.

Note : However the dark theme may not be applied in some apps and Home/lock screen.