OnMouseEnter is blinking

Hello ! Since the last 4 days, I'm working on a script highlighting . When my cursor is over a special object, I apply a special effect to it.

My problem is that I use the function OnMouseEnter and OnMouseExit to make it work but they are "blinking", the effect don't stop to appear and desappear.

Here's my code :

 private Shader normal;
 private Shader hover;
 private Renderer renderer;

 void Start()
 {
     renderer = GetComponent<Renderer>();
     normal = Shader.Find ("Standard");
     hover = Shader.Find ("FX/Gem");
 }

 void OnMouseEnter()
 {
     GetComponent<Renderer> ().material.shader = hover;
 }

 void OnMouseExit()
 {
     GetComponent<Renderer> ().material.shader = normal;
 }

My last solution is to change my code to a Raycast system... But I prefer to ask you before to change.

(Sorry for my poor english..)