Todel,
In my experience, it depends on what you are trying to change.
Sometimes when you are done with your description and you preview your listing you need to go back to the description and highlight the unchanged text and manually change it. If you go to white you won't be able to see it in the editor...only in the preview.
Some items I have not been able to change (the Bidpay HTML and the ebaycounters HTML that I use). If you are good with HTML you could probably change it, but I'm not that computer literate. What I do is highlight those items and put a white background (or the appropriate color depending on the template I'm using) behind it. It looks sort of cheesy, but it is easier to read once it posts to eBay.
Hope this helps you out a bid.