change the colour of the object when mouse is over the object

[system]

How can I change the material of the object if there is a mouse placed over that 3D object. I've seen the dragObject script but I don't want to use RigidBody although I am just going to use simple collider for that..

[system]

An easy solution would be to use OnMouseOver. Example code to set to red when mouse is over:

var initialColor : Color;

function Start()
{
   initialColor = renderer.material.color;
}

function OnMouseOver()
{
   renderer.material.color = Color.red;
}

function OnMouseExit()
{
   renderer.material.color = initialColor;
}

Alternatively, you could raycast from the camera position to the mouse position. The benefit of the Raycast is that you can specify a layerMask (to only hit objects on a given layer).

function Update()
{
   var hit : RaycastHit;
   var ray = Camera.main.ScreenPointToRay (Input.mousePosition);
   if ( Physics.Raycast( ray, hit, 100 ) )
   {
      if ( hit.collider.gameObject.renderer )
         hit.collider.gameObject.renderer.material.color = Color.red;
   }
}

In these examples, the color of the renderer material is explicitly set to red when the mouse is over it, but you can change it according to your needs.