Flag Cancellation, Is It A Valid Cancellation ?

Not just the paper color. Bluish paper contains some rag stock unlike normal stamp paper of the time made from 100% wood pulp. So called "China Clay" papers, delisted from the Scott catalog, were normal paper contaminated with silica from muddy water used to make paper during times of low water.

Clark

It is best if you look at the back of your 5c stamp. The stamps of this era often ave a background haze of the stamp ink (due to imperfect plate wiping) and since your stamp is blue, you might confuse a blue haze as blue paper (and you are really looking for grey paper - blue is not the real color although we seem to be stuck with the name).

Thanks for the informations.
But if somebody can place a scan of the back of a bluish paper stamp, I thank him very much.

We have explained to you how to identify the 'blue' paper variety. Find a piece of orange paper and scan the stamp(s) laying on the paper (face down). Post the images.
You also should learn how to search this forum since 'blue paper' has been covered extensively before. Click on 'Search' button and type in 'blue paper' and search. You will find many images of blue paper examples (including using orange paper as the background)
Don

Priatel, if you search for "bluish paper", you will find a thread by 'martinboyanov83' called "bluish paper ???".
That thread is excellent. It has pictures of the back of stamps on bluish paper. You can search by clicking the "search" box on top of this page!

Peter

I found the posts.
Thank you