Scott 344 Imperforate 2 Cent Carmine

I need to know how to see the Double Line watermark on this one. Could someone be so kind as to explain to me? I have looked at it carefully and maybe I just do not recognize the Double Line.
Also, does Double Line watermark paper feel or look different than the later Single Line watermark paper.
What is the "blue" paper? Is it gray or blue. Tell me something about it please.

Thank You

There are revenue/fiscal stamps printed on blue paper that is actually blue. However, the 1909 "Bluish paper" stamps of the US are really much more gray than blue. They are caused by the bureau using rag paper in an attempt to reduce the shrinkage of the sheets and the resulting difficulty in getting decent perforations.

Also, best seen by putting the stamp on an Orange background. Put two examples next to each other under a good light for best analysis.