Code for a simple color controlling web page

<html>
<head>
<style>
body {background:#F00}
</style>
</head>
<body>
<p>Red on full, green off, blue off.</p>
</body>
</html>

A variation of the above as seen in gEdit:
Gnome gedit in action

Other background colors to try:
body {background:#0F0}
body {background:#F00} /* Those are ZEROS not the letter "O"! */