Haha...I found the way to make all of em Transparent back ground white when using viewers.
In PDN, even if the black ground showing it's Transparent, when saving as png, sometimes show white back ground and sometimes show black.
To get all of em white, just use magic wand to select all the Transparent areas and hit Delete.
Save file again.....Now all the black "Transparent" area turns to white in image viewer.
Strange....but it works. 8)