I see that the getCategoryList now (14R2) returns the backgroup color if it
is set.
Now I still have a problem:

When the background-color is not modified for a category the background
color it is not in the soap response.
My Soap2Object module creates a list of category objects where the
background color is set to 0 if the backgound is not in the xml for a
category. (I thi