GET GREASY (https://www.kirupa.com/html5/creating_a_strobe_light_generator.htm)

strobe.js

var bodyElement = document.querySelector("body");

var requestAnimationFrame = window.requestAnimationFrame || 
                            window.mozRequestAnimationFrame || 
                            window.webkitRequestAnimationFrame || 
                            window.msRequestAnimationFrame;

var delay = 0;

function changeColor() {
	delay++;
	
	if (delay > 3) {
		bodyElement.style.backgroundColor = getRandomColor();
		delay = 0;
	}

    requestAnimationFrame(changeColor);
}
changeColor();           

function getRandomColor() {
	// creating a random number between 0 and 255
	var r = Math.floor(Math.random()*256);
	var g = Math.floor(Math.random()*256);
	var b = Math.floor(Math.random()*256);
	
	// going from decimal to hex
	var hexR = r.toString(16);
	var hexG = g.toString(16);
	var hexB = b.toString(16);
	
	// making sure single character values are prepended with a "0"
	if (hexR.length == 1) {
		hexR = "0" + hexR;
	}
	
	if (hexG.length == 1) {
		hexG = "0" + hexG;
	}

	if (hexB.length == 1) {
		hexB = "0" + hexB;
	}

	// creating the hex value by concatenatening the string values
	var hexColor = "#" + hexR + hexG + hexB;
	return hexColor.toUpperCase();
}