I think what you want should be do-able using an HTML form. Something like the following:
<form action="blah.php">
<select name="variableName">
<option value="green">green
<option value="red">red
<option value="yellow">yellow
</select>
</form>
Then in blah.php,
$body = "Color selected is ";
$body .= $variableName;
mail($to, $subject, $body);
If the selection made in the form was "yellow", this assigns the value "yellow" to the variable $variableName by naming that to the select tag. Wherever the action to the form is takes that name ($variableName) and its value. You can place it into a $body string to formulate the e-mail, and your output will show "Color selected is yellow"
Hope this helps.