In some cases, you might have a document that contains white text.
By default, PDF2XL changes the color of that text to black, but you can change the color of that text to a variety of other colors.
Go to Options > Format and find the feature "Change white text's color to:".
You can select a different color for your white text.
If you want to see this change in the preview, you may have to refresh the Preview sizes, colors option by deselecting it, then selecting it again. Note that you do not need to have this option selected for the converted document to retain the color.
If you still can't see the color change, go to Options > Conversion and make sure you have "Keep text attributes" selected.
When you convert your file, your colored text should appear: