I'm sure this is really simple and I'm drawing a giant blank, but how do you set the result of a function as a global variable?

Example, I want to set the first color in array colors as global variable color (I know the example doesn't make much practical sense, but it's just to illustrate my question):

var color = ;



function selectColor () {

    var colors = [blue,red,green,yellow];

    var color = colors[0];

    return color;

}



window.onload = function () {

    selectColor ();

    alert(color);

}