Transparent layer between pdf widget and field?

[doc hawk]

As I’ve had to build every form myself in the past, they were constructed of fields, lines, and boxes.  As such, with them not being opaque, I could put a rectangle behind the group that was turned visible when the group was active, as a visual  cue.

Now that I’m using pdfs, this isn’t working as well, as I have fields laying over the pdf in many cases.

Is it the colorOverlay property I need to do, with my rect above the pdf and below my fields?

I want the pdf visible enough to read, but the fields in front of it.