It depends on the criteria.
If the criteria is a specific value, you may be able to put this value in a global field or global variable and use a conditional format expression to change the fill color of the matching portal row fields.
If the criteria is more complex, you might need to freeze the window and separately search the portal's table on another layout and load a global field or global variable with recordID's or serial numbers of matching portal records. Then you can return to the layout and your conditional format expression can highlight the fields if the portal record's recordID or serial number is a member of this list of values. (You'd use the FilterValues function to check against the list here.)