It would be possible yes.. something like this.
PHP Code:
<?php
if(!$_GET['color'])
{
$color = "blue";
}
else
{
$color = $_GET['color'];
}
?>
<img src="http://www.www.www/images/<? echo $color; ?>_01.gif">
It would work, but would be a little limited unless you expanded it quite a bit. Also, you could even set a cookie to remember it for when people come back. I would personally use the one I stated above, as it would be more versitile (It would allow completely different interfaces totally), however, this would work also.