highlight objects which are visible in camera?

Hi friends, I am trying to make a 3d model overview in which user can rotate camera around it and can see different parts of that model. I have problem with front and back side parts highlighting because I want to highlight only front part when camera is at front side, and back side parts when camera rotates to that side and I have used the OnBecameVisible() and OnBecameInvisible() and renderer.isVisible but all of these are not working well in my case. So please suggest me some proper way. Thanks in advance. :)