var colors = Array("green", "red", "orange", "blue", "gray");
	
function overlay(colorGiven) {
	if (colorGiven == null) {
		colorGiven = "gray";
	}
	for (i = 0; i < colors.length; i++) {
		if (typeof(document.getElementById(colors[i]))!=='undefined') document.getElementById(colors[i]).style.display = "none";
		if (colors[i] == colorGiven) {
			document.getElementById(colors[i]).style.display = "block";
		}
	}
}