When using Interactive fields in PDF, the filler is then expected to enter data inside of the fields in the preview window. The thing is that these fields have a very neutral look and may easily be overlooked. So if you wish to have them stand out - and make it easier for the filler to notice them - you can have them highlighted.
* and again...thanks... Gal S. all cloud :-)
Watch how to highlight your interactive fields
Enjoy!