You could use some php code in the binding for field 3:
<?php echo((($_POST['field1_form_field'] == "1000" || $_POST['field1_form_field'] == "2000") || ($_POST['field2_form_field'] == "2" || $_POST['field2_form_field'] == "3"))?"red":"green"); ?>
I'm assuming you are inserting the values for field1 and field2 on this page as well, but basically you need to write an if statement like this one to achieve that result.