I found this in a mystery I'm reading. The book is The Seventh Witch by Shirley Damsgaard, one in a series where the detective and her grandmother are witches and have supernatural powers.
"When I'd commented on my sound sleep, ... Abby informed me that my quilt could be thanked for my restful night. The bold blue and yellow rosettes pieced together with muslin, now aged to a pale ivory, were really hex signs. The rosette was the sign for good luck ... blue the color of protection, and yellow the color of health."
I don't think the rest of the book has anything to do with quilting, but it made me curious. Has anyone heard of this, of magical or supernatural meanings assigned to designs or colors? Do you know of any other references to it?