Transform.ColorTransform

I have an object, when I shoot a laser at it, I want to change the color to red, delay for a second and then switch back to the normal state(no red);

so
var redTint:Color = new Color();
redTint.setTint(0xFF0000,1);
myObject.transform.colorTransform = redTint;

this works fine, however when I try to reset back to it’s normal state with:

myObject.transform.colorTransform = null,

I get this message **Parameter colorTransform must be non-null.

**Any ideas