If you wish to have revised PO's appear in a different colour on DPO then the admin can enable this option by doing the following:

Admin > P.O Settings > Check 'Use alternative Colors for revised PO's' > Save and Next at the bottom of the screen.

If a PO is then revised the colour will change to a light blue like shown in the below example when pending/ pending approval:

Once the revised PO has been final approved the colour will change to a dark blue like shown in the below example: