The default text color is the color of the first text item on the page... This is not necessarily the text item that appears topmost on the page
The most straightforward thing to do is this:
- Select one of the text items on the page, then click the "fill" button in the top toolbar and make it white (for example).
- Right-click this white text item and select "Order -> Send to Back".
That should do it - if you preview the site, the text will be white.