a. Check whether “Eye comfort mode” is active. Eye comfort mode will filter out blue light and adjust the colour temperature of your display to reduce eye strain.
1) Go to “Settings”->”Display”-> “Eye comfort mode”->touch the trigger to activate /deactivate it.
2) Drag down quick settings bar in any interface ->touch "Eye comfort mode” icon to activate/deactivate it.
b. In reading mode, the screen will become monochromic to imitate physical books. Go to “Settings”->”DISPLAY ENHANCEMENT”->”Reading mode”, touch the trigger to activate/deactivate it.