Bill,
It is my understanding that "sugar paper", so called because it was used to wrap cones of sugar called sugar "loaves", was made from cloth dyed with indego dye . Indigo dye is unusual in that it does not require a mordant, and was raised as a crop and processed commonly on plantations in tropical areas.
The blue paper that it produced when the dyed cloth was beaten and formed into paper is very close in color to the blue background on this site postings, at least on my monitor.
It was traditionally used for many of the documents related to the indentured servants ( really more like post-slaves) in the official Chinese system of laborers transported to work in the Cuban sugar industry in the 1800s, and I have some such original; documents in my collection.
I know that you can purchase reproductions of the traditional sugar loaves wrapped in blue paper and wax sealed, but not whether this paper is authentic.
Karl