You'll need to describe this in more detail first.
What is the conditional format expression you are using?
If the conditional format refers to data in related tables, how are those relationshps defined?
And what is the relationship between the layout's table occurrence and the portal's table occurrence?
You need to use a field and set the fill color to none. Then set your condition formating. You will have to change the opacity so that you will be able to view the fields behind the highlight field.
You change use conditional formating for the fonts in each field also. When I view all records on a portal, I set the font to red on inactive accounts.
I think I figured it out as I was using a formula involving a related record, so I ended up adding a calculated field on my portal table and now it seems to work as desired.