Samsung cell phone display become colorless

Can you upload a photo of how the screen looks like?

What settings if any did you change?
Is it dimming?
From Samsung
To adjust the brightness of the display, access the Brightness settings menu. From the Home screen, touch Menu  > Settings  > My device  > Display  > Brightness.
Mark the box for Automatic brightness to let your device adjust the display brightness using its sensors.
To manually adjust the brightness, touch and slide the bar to the right for a brighter screen, or touch and slide it to the left for a darker screen.

You can also adjust the brightness level from within the Notification Panel.
Swipe your finger from the top of the screen to the bottom;
the display brightness adjustment bar is shown just below the Quick Panel shortcuts.
 Touch Auto to turn on Automatic brightness.
See also
Why does my GS4 screen randomly dim?

Colorless and dimming are two different things.

Colorless can be the results of adoption of extreme power saving plans to make the display to be shown as gray scale,

I think you are right jackie. It is colorless instead of dimming
How can I get it back? Thank you

Great! Thank you

Thanks for your feedback.

Glad to know that you have solved the problem. Cheers!