@MEB: There is no "File -> Document Setup" option. Menu items
I can't figure this out either.
1. Import image with background.
2. Select, using magic wand tool, all colored space (background is black).
3. Document=>Transparent Background. {Nothing Happens}
4. Export this image with Transparent Background checked. Unmodified image exported.
5. Open Export Persona.
6. No PNG-24 transparency option.
7. I give up.
OK, I see that the first box represents "font color" though the only way you can discover this is if you serendipitously hover over the box. This fixed the problem, thank you.