Although I've never used it, it seems you could have and maintain an attribute of the object which acts as a flag, and use Item Display/Presentation Rules with appropriate criteria.
OR, in the RegularUser object have a separate attribute for each query for which you want to highlight the last added record. Then update the corresponding attribute with the ID of the last added record when the form is saved.
Then in the query Item Display/Presentation Rules the criteria for the highlight (different background color) would be:
objectname.ID=LoggedInRegularUser.objectname_lastaddedinstanceID
And if you only want to highlight the last added record during the 'session' in which records are being added for an object (ie. not highlight it a week later when next login occurs or 10 minutes later after the user has gone and done something else and then come back to the query) then you could just use one attribute in RegularUser to manager it.