When trying to change the background color of a reference field, the following does not work:
g_form.getControl('reference_field').style.backgroundColor = 'red'
The above will work for other field types, except not for reference fields.
The getControl() method is not appropriate for reference fields.
The right method for reference fields is getDisplayBox(), like so:
g_form.getDisplayBox('reference_field').style.backgroundColor = 'green'