Yesterday there was one customer who complained that the appearance of his android screen suddenly turned black and white, or gray, I was also confused because he was the first time seeing a screen of an Android phone that turned gray.
To correct the above problems please follow these step. First, please try to open your Android Settings / Settings menu then please try to find the accessibility menu there later you will find options for Vision or Invert Colors, there may be other options but I am sure there are other terms for each Mobile phone factory. if there please please uncheck or select just turn it off.
Finished. Hopefully it can help resolve your problem. May be useful.