Why doesn't my script work?

So basically i created a script that will toggle whether or not the camera’s image effect grayscale will be toggled… I don’t care about the actually “isGrayscale boolean” as of yet… I am more interested in the actual toggling of the button Textures… Basically when i click the button on-screen, the texture changes from the standardButton, to the buttonChecked… But when i click it again, it just won’t work?? Here is the script:

var standardButton : Texture;
var buttonChecked : Texture;
static var isGrayscale : boolean = false;
private var isChecked : boolean = false;

//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

function OnMouseDown () {

	if(isChecked == true){
		isChecked = false;
		isGrayscale = false;
		renderer.material.mainTexture = standardButton;
	}
	
	if(isChecked == false){
		isChecked = true;
		isGrayscale = true;
		renderer.material.mainTexture = buttonChecked;
	}
	
}

//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

try a else statement after the first is checked instead of checking if its set to false, because at the moment as soon as you set ischecked to true it gets set to false automatically then it loops back & forth.