There is one junction object in which one master object has owd public access and one master object has private access
The first master-detail relationship you create on your junction object becomes the primary relationship. This affects the following for the junction object records:
Look and feel: The junction object's detail and edit pages use the color and any associated icon of the primary master object.
Record ownership: The junction object records inherit the value of the Owner field from their associated primary master record. Because objects on the detail side of a relationship do not have a visible Owner field, this is only relevant if you later delete both master-detail relationships on your junction object.
The second master-detail relationship you create on your junction object becomes the secondary relationship. If you delete the primary master-detail relationship or convert it to a lookup relationship, the secondary master object becomes primary.
For reference check this article.