HTML
<div class="one_in"></div>
CSS
.one_in{
width:100px;
height:100px;
border:1px solid #000;
}
JS
var ar = ["one_in", "two_in", "three_in"]; 
var colors = {
    ar[0]: 'blue',
    ar[1]: 'green',
    ar[2]: 'red'
};
x = document.getElementsByClassName('one_in');
for (var i = 0 ; i < x.length ; i++ ){
    x[i].style.backgroundColor = colors[x[i].className];
}
How to use the array ar's value "one_in", "two_in", "three_in" inside the object so my div get automatically colored in blue green red respectively 
http://www.w3schools.com/code/tryit.asp?filename=FAYMJN2T8KU2
 
    