When viewing addresses in a userprofile there are 2 DIV's:
default adress if it has been set
list of addresses if there is more than one
There 2 DIV's are always there, even if they are empty.
So if a coloured background has been defined in css, and a customer has only 1 address set, there is a blank coloured box. If the one address is set as default the box #commerce-addressbook-billing-list will be empty and if not the #commerce-addressbook-billing-default will be empty (but still displayed. It would be good to have them only be displayed when they are not empty and it might be good to set the address as default if there is just one.
With kind regards