Changes the background color using setInterval. Pretty old school though, better to use requestAnimationFrame to not completely destroy the battery life of mobile devices

naiveColorChanger.js

  		var intervalTicks = 100;
			var redValue = 1;
			var greenValue = 1;
			var blueValue = 1;
			var colorChangeMagnitude = 1.01;
			var backgroundColor = "rgb("+redValue+","+greenValue+","+blueValue+")";
			var redFlag = "down";
			var greenFlag = "up";
			var blueFlag; "up";

			window.onload = function()
			{
				initColors();
				setInterval(changeBgColor, intervalTicks);
			}
			
			function initColors() {
				redValue = Math.floor(Math.random() * 255);
				greenValue = Math.floor(Math.random() * 255);
				blueValue = Math.floor(Math.random() * 255);
				changeBgColor();
			}

			function changeBgColor(){
				if(redValue < 100)
					redFlag = "up";
				if(redValue > 200)
					redFlag = "down";
				if(redFlag == "up")
					redValue *= colorChangeMagnitude;
				if(redFlag == "down")
					redValue /= colorChangeMagnitude;
				
				if(greenValue < 100)
					greenFlag = "up";
				if(greenValue > 200)
					greenFlag = "down";
				if(greenFlag == "up")
					greenValue *= colorChangeMagnitude;
				if(greenFlag == "down")
					greenValue /= colorChangeMagnitude;

				
				if(blueValue < 100)
					blueFlag = "up";
				if(blueValue > 200)
					blueFlag = "down";
				if(blueFlag == "up")
					blueValue *= colorChangeMagnitude;
				if(blueFlag == "down")
					blueValue /= colorChangeMagnitude;

				backgroundColor = "rgb("+Math.floor(redValue)+","+Math.floor(greenValue)+","+Math.floor(blueValue)+")";
				document.body.style.background=backgroundColor;
			}