Why doesn't GUI disappear after I leave trigger?

Hi, I have written this code which displays a GUI image when the player enters a box collider. However, I want the image to disappear once they have left the box collider. I thought that I was doing this with the else statement, as I have created a blank image called "clear". (However if you know of a way of doing this without using an image that would be good)

var Blank : Texture2D;
var Crouch : Texture2D;

function OnTriggerEnter(otherCollider : Collider) {

    var g_infotext = gameObject.Find("g_infotext");

    if (otherCollider.tag == "ColliderCrouch") {

     g_infotext.guiTexture.texture = Crouch;

        }

    else {

        g_infotext.guiTexture.texture = Blank;

    }

}

Thanks

It's quite simply, really, as all you have to do is use a `boolean` variable and an `OnTriggerExit` function as well as an `OnTriggerEnter` function. The following code should do the trick:

var Crouch : Texture2D;
var canShow = false;

function OnTriggerEnter(other : Collider) {
    var g_infotext = gameObject.Find("g_infotext");
    canShow = true;

    if (other.gameObject.CompareTag ("ColliderCrouch") && canShow) {
        g_infotext.guiTexture.texture = Crouch;
    }
}

function OnTriggerExit (otherCollider : Collider) {
    canShow = false;
}