White boxes with opacity less than 100% appearing as gray instead of white

[Jason Teague]

I use Vectorworks CAD software in my business for production of construction drawings.  We sometimes use white translucent rectangles to visually subdue some areas of a background drawing.  A current drawing set that has been published has several of these white translucent rectangles.  They are appearing a gray translucent boxes which makes the drawing more difficult to read and clunky.  Other pdf readers are rendering these boxes correctly as white boxes, but Nitro Pro is rendering them as gray.  I don't remember seeing this problem before.  What can be done to resolve?  This is problematic.