Thank you, Post_pe.
I see them being more reddish than red. If you mean the red spot at the top perf hole and points below, that looks like staining or adherences.
Granite paper is the result of the deliberate addition of chopped colored threads as a security feature. Therefore, the pieces are made to be seen. There could
be cases where a stamp could have no trace of threads. That said, the fibers shown here are too fine to be considered granite paper and are accidental impurities, in my opinion. Even then, a colored thread or two does not make it granite paper. Paper is not made under laboratory conditions after all.
If you have a USB microscope or similar, examine the fibers. If not ribbonlike and are in brown or grayish or blackish, they are likely a natural wood fiber that escaped or resisted bleaching.
The same issue comes up with early US revenues on what is called silk paper. There are quite a few collectors who see fibers that are accidental additions and not intentionally included and think it is silk paper:https://revenue-collector.com/1stis...papers.shtml