Here's an easier way to make the text invisible:
Use conditional formatting to change the font size instead of the color. For a single row text object in the 10-12 point range, a size of 120 or larger is enough to make the text disappear.
This will not work for large "paragraphs" of layout text, but works very well for single row text objects.
For large blocks of text you may want to consider placing the text inside an invisible tab control and manipulating the tab control to hide/reveal the text.
Thank you for an alternative tool. If I follow this correctly, it works fine for text in a field (or it did for me and I like it). However, I want to conditionally hide and reveal a text object that is not a value in a field. When I try this technique on that type of text object, the text is just displayed in a large font.
Please clarify if I am missing something.
Also, I would repeat the original question. Does anyone know how to find (or copy) the color definition of the background in themed layout?
Layout text can also be made to disappear with this method. That, in fact, is the most typical object that I make conditionally visible with this method.
Take a look at the FMP Bugs layout in the Known Bugs List Database. Note the delete portal row buttons in each of the three portals at the top of this layout. These buttons are just a bold face letter X bit of layout text with conditional formatting to make them disappear off the bottom "add" row of the portal to make clear that there is no record to delete in that portal row.