blink the screen

When the player is hited by enemy’s bullet how to make the screen flashes for few seconds to show that player lost his energy.When ever player is hitted by bullets screen should flash for few seconds before screen comes to normal.can you please provide solution in C#.How to make screen blink using gui or any other solution.

What do you mean by blink? What comes to mind is changing ambient light (Unity - Scripting API: RenderSettings.ambientLight) or messing around with the Camera Fade system from the iTween library (iTween for Unity by Bob Berkebile (pixelplacement)).