GUISkin question

I download the Asset Store “NecromancerGUI”,
I want to use it GUISkin. but no effect. why?

var skin:GUISkin;
function OnGUI () {
    if (skin != null) {
        GUI.skin = skin;
    }

You have a typo.

var skin : GUISkin;
function OnGUI () {
    GUI.skin = skin;
}

Your variable is called skin, but you were trying to reference skins which doesn’t exist. You also don’t need to check it for null since when GUI.skin is null, it’ll use the default skin anyways.