While in layout mode, select the portal field.
In the status area, click the Aa button if the formatting bar isn't visible.
On the top right are fill and pen colors and patterns.
Select the Transparent Fill pattern (Top left square in the pattern palette) and you're done.
When working with the portals, you can resize the portal row to be tall enough that you can place layout text above or to the left of a field if you wish. Simply click on the portal while in layout mode and drag the small black squares (selection handles) to resize the portal rows (or enter a different height in the height box on the position tab of the inspector (filemaker 11).
That worked great!
Nice answer for first part; no answer to second part re portal field labels. The subsequent post re Portal Field Labels only works on occasion for me eg.
double click field and select label. When moved to field over column will not necessarily be there after saving and changing to browse. By the same token selecting text, creating box and typing the label won't consistently work. Yes, it will SOMETIMES. What is the other condition necessary to make this work consistently? Thanks.