this is pretty much for my own info- I just bought some officials and am learning about them- I was browsing and am practicing on your question- forgive the intrusion...just passing through.
your O17 or O98 3c washington seems to be in the same boat
the thin/hard paper O17 or O18 of 1873 Vermilion it says in the postal guide to us stamps it is PERF.12 Non Watermarked.
the soft porous O98 or O99 1879 Vermilion it doesn't mention PERF. or Water Mark.
-----------------this is the deciding mark for me---------------
the 1873 were supplanted 5/1/1879 by penalty envelopes (which it appears your stamps are on a penalty envelope) so I would guess your stamps are of 1879, O98 3c and O99 6c. (7/5/1884 were declared obsolete.)(unless it is totally messed up where they allowed 1873 issues to be used on the 1879 penalty envelopes along with the 1879 issued stamps-they should have caught it and disallowed the 1873 usage on the penalty envelope)(how would they know which stamps they were 1873 or 1879? -->by paper type)
specialty catalog has colors
O17 3c vermilion,dull vermilion or bright vermilion.
O18 6c vermilion,dull vermilion, bright vermilion or scarlet vermillion.
O98 3c vermilion or pale vermilion
O99 6c vermilion,pale vermilion or scarlet vermilionhttp://www.1847usa.com/BanknotePaperTypes.htm
i read this link on paper it seems to head us in the right direction and maybe even our UV lights can help but it gives examples on other stamps that you might not have attached to the envelope to practice on to determine what paper you have.http://people.csail.mit.edu/jaffer/Color/S.htm
i just threw in this color chart it was interesting for vermilion but confusing too. Makes sense that charts are not much help due to age and fading.
lastly learned how to spell vermilion one L
ugh time for a break