var post_ad = $('.duplicate_name');
var post_ad_cloned = post_ad.clone().removeClass('duplicate_name').appendTo('#sss').show();
$("input", post_ad_cloned).css('color', 'red');
или:
var post_ad = $('.duplicate_name');
var post_ad_cloned = post_ad.clone()
.removeClass('duplicate_name')
.appendTo('#sss')
.show()
.children('input')
.css('color', 'red');