var rndColor = '';
    var randomColor = function (rndColor) {
        var colors = ['red', 'blue', 'black', 'white', 'green', 'yellow', 'purple'];
        var rndColor = Math.floor(Math.random() * colors.length);
        return rndColor;
    };
    randomColor(rndColor);
    console.log(randomColor(rndColor));

var randomColor = function () {
        var colors = ['red', 'blue', 'black', 'white', 'green', 'yellow', 'purple'];
        var rndColor = Math.floor(Math.random() * colors.length);
        return colors[rndColor];
    };
 
    alert(randomColor());