Jquery auto change class on div

I have a div with class .render-inner.render-letter and I made with jquery to add classes (red, blue, green, yellow) to the existing one (.render-inner.render-letter yellow , .render-inner.render-letter blue ...) with a click of mouse. How do I make classes constantly change without a mouse click and without stopping?

here is code:

$(document).ready(function(){   
        $('.render-inner.render-letter') .addClass('green');        
var classes = ['red','blue','yellow','green'],
        i = 0;
    $('.render-inner.render-letter').click(function(){
        $(this).removeClass(classes[i])
               .addClass(classes[ i = ++i % classes.length ]);         
    });
});

Thanks :)