How to rotate through a selection of colors - Appcelerator Titanium

app.js

var win = Ti.UI.createWindow({
  fullscreen: true,
	backgroundColor: 'blue',
});
 
setInterval(function(){
	var backColor = win.backgroundColor;
	if(backColor == 'blue'){
		win.animate({backgroundColor: 'purple', duration: 1500});
				win.backgroundColor = 'purple';			
	};
	if(backColor == 'purple'){
		win.animate({backgroundColor: 'red', duration: 1500});
		win.backgroundColor = 'red';		
	};
	if(backColor == 'red'){
		win.animate({backgroundColor: 'orange', duration: 1500});			
			win.backgroundColor = 'orange';		
	};
	if(backColor == 'orange'){
		win.animate({backgroundColor: 'yellow', duration: 1500});			
		win.backgroundColor = 'yellow';		
	};
	if(backColor == 'yellow'){
		win.animate({backgroundColor: 'green', duration: 1500});		
		win.backgroundColor = 'green';		
	};
	if(backColor == 'green'){
		win.animate({backgroundColor: 'blue', duration: 1500});				
		win.backgroundColor = 'blue';		
	};
 
	backColor = win.backgroundColor;
	}, 2000);
 
win.open();