You need to be
extremely careful buying stamps like these on
ebay. I don't normally buy stamps (I collect covers) but the ones that I do (24c 1861s) are incorrectly listed on
ebay more often it seems than they are correctly listed.
Last I looked I'd say that probably 40-50% of the Steel Blues on
ebay, including the majority of them offered without PF/PSE certs, were color changelings and not true Steel Blues (70b).
It's almost comical if it wasn't so scary. You see "#70"s opn cover used in 1866, Steel Blues with 1867 year date cancels, people making a big deal about red cancels on 24c 61s (Which are remnants of exchange office markings, which were always red if the mail was prepaid and seeing as the extreme majority of these stamps were used on foreign mail.....), ad nauseum.
Take a peek at scads.org