potresti provare così:

function setBackgroundColor(color) {
var body=new array();
body[0]=document.getElementById('SottoMenu1');
body[1]=document.getElementById('SottoMenu2');
body[2]=document.getElementById('SottoMenu3');
var background = "#FF6C6C"; // default
if (color == 1) background = "#FF6C6C";
if (color == 2) background = "#82AAFF";
for(i=0;i<body.length;i++){
body[i].style.backgroundColor = background;
}
}