Woww... ERP 4.91 seems so old and antique now --- Do not recollect / remember -- but IF IT IS not working than this "attribute" might not have been introduced in that version. Hence it will not work. As one can see from screenshot it is working in later versions.
It will not show in Preview mode --------- for some reason the BORDER colors have been excluded from preview. My screenshots above also shows in Exported docs but not in preview mode.