US First Issue Revenues - Color Of Threads In Silk Paper?

I know that most threads in the first issue silks are blue. Are there red threads as well?

There sometimes are, but they are not "silk threads". Remember that we are discussing 1862-1871 paper here, and quality control was just a dream. Also remember that the paper went from very thin hard mostly rag paper to thick soft mostly wood pulp paper. From multiple vendors. And there was a lot of urgency during the length of the issue; the tax money was desperately needed. So there was a lot of "dirty" paper used, often with fibers and inclusions from the papermaking process. True silk paper was not used until 1870.

Thanks revcollector