THE GUYS OVER AT DIGITAL FUSION have found an easy way to get rid of the grey/black color that appears when you run your mouse over a portal row using the Active Row State feature:
How can we do this
The first thing you need to do is to go into the portal setup and tick the “Use active row state” option. This may seem counter-intuitive – surely you would want to disable the active row state in order to prevent any fill. In actuality, keeping it disabled gives the default grey fill behaviour.
There are a lot of gems yet undiscovered in FileMaker 13. Bonus–download file at the link.