Hi Ron. You can do this by opening the Mosaic Plot Properties, selecting the area where you want the white text, then changing the Text Color. You can change other fonts or backgrounds selectively this way, too. I tried it using the Car Poll Data from the Sample Library.
1. From the Mosaic plot, Right Click Mosaic Plot Bar then select Edit>Show Properties. This will open the Properties Window.
2. Left click to select the area where you want to change properties. Then in the Properties Window, Left Click the Properties>Edit>Text Color. Select the white color you want. When you Left Click on the Mosaic Plot, the text colors will change.
3. Close Properties box and copy/paste or save plot as needed.