Some issues vary in color greatly amongst themselves, as there was often shortages on consistent ink supplies during the Civil War. Early revenues are often found with various types of cancellations. Truly mint copies are a challenge to find. Stamps are often canceled with manuscript handwriting, hand stamped with a private cancel, pre-canceled with a private provisional company cancel and punch canceled. Later revenues are also found with perforated initial cancels.
Varieties also exist in the perforations.
Stamps with large clear margins always demand a premium as do copies in multiple formats. They are desirable as they cover interesting occupations. They are intricately engraved with large vignettes and vary in color by the year issued. For example the Peddler Third Class stamp covers the annual fee for a peddler of tobacco who travels with one horse, mule , or other animal. Revenue stamps are a wonderful collecting avenue to take.