<!DOCTYPE html>
<html>
<style>
div {height:50px;width:100%;}
</style>
<body>
<h1>Gray can be set using equal values for all light sources</h1>
<div style="background-color:#000000"></div>
<div style="background-color:#404040"></div>
<div style="background-color:#808080"></div>
<div style="background-color:#c0c0c0"></div>
<h1 style="color:#000000">Heading</h1>
<h1 style="color:#404040">Heading</h1>
<h1 style="color:#808080">Heading</h1>
<h1 style="color:#c0c0c0">Heading</h1>
</body>
</html>