The different coloured boxes would be an easy way to signify which shelves are mine and which are yours. And you could use the spaces on top of the boxes for the things that you share.
And here’s a fun bonus idea. These ‘legs’ are made by attaching a string of pastel wooden baubles to the bottom of the cabinet. Just drill a small hole in the bottom of the shelf, thread the twine through and loop it around a wooden washer to hold it in place.