function change(i) {
var doc = document.getElementById("background");
var color =[ "black", "blue", "brown", "green"];
for(i=0; i<color.length; i++){
doc.style.backgroundColor = color[i];
alert("my color is "+ color[i]);
/*if (i>=color.length){i=0;}*/
}
}
setInterval(function changebackground(){change(0)},1000);