I have a small study group of admission tickets for the Centennial Expo of 1876, and I thought some of you might be interested in looking a bit more at their varieties. These tickets were lithographed by the Philadelphia Bank Note Co., which was a successor firm owned and managed by the earlier revenue producer, Joseph R. Carpenter.
The tickets come with a bit of variety, three colors of backs and various treatments of the secondary obverse printing.

The most common tickets have a "white" or uncolored reverse.

These are the only ones which show the diagonal obverse overprint, "FIFTY CENTS" instead of the admission fee as part of the design. This overprint most commonly occurs in carmine, but is also known in black. The ticket numbers are most often in carmine or blue, but do occur in black as well.
Tickets with a pale blue-green network print on their back are not as common as their white-back cousins, and do not have an obverse overprint.

Instead their obverse design now bears the words, "FIFTY CENTS" just below the central panel with the words, "PACKAGE TICKET." Ticket numbers usually appear in carmine or blue, but a few appear to have been printed in ultramarine.
The least frequently seen variety of these are those with a reddish-pink network overprint on back, which may appear as pale or moderately deep.

The obverse design on these has the same features as the
blue-green white-back type, but without a value overprint. For the "pinks" I have only seen the ticket number printed in carmine.
[Edit: I messed up the last description.]