Cultural tradition would certainly be helpful.  Here in the southeast a lot
of people have been looking at the significance of blue in African-American
traditions as well as ceremonial-type burials of items within houses.  Try
Patricia Samford's work.  Linda Stine has also done a lot of work in this
area.  I can provide a phone number for Linda, but I don't think she has
access to internet.
 
L. Wayne