For display at the Atlanta International Cotton Exposition (October 5th to December 31, 1881), the government had the American Bank Note Company print full sheets of all U.S. stamps designs produced to date (including Officials, but excluding revenue stamps). Five sheets of each design were printed on thin white cardboard in each of five colors: red, blue, green, black, and brown.

106TC Atlanta Trial Color Proofs
(Scan courtesy James Lee)

Bi-color stamps such as the 1869 series and the high value State Department stamps were printed in up to 14 different combinations of colors.

Scans of 15c blue/black and blue/brown courtesy James Lee
Scans of 15c green/black and 90c black/brown courtesy Siegel Auction Galleries

While these are generally referred to as Trial Color Proofs, they are actually government commissioned reprint proofs. Arguably, these could be classified as "cinderellas" or "fantasy stamps" although they are de rigeur items for exhibitors wishing to display a "complete" exhibit of any particular issue up to and including the stamps of 1875.

These sheets found their way into the hands of collectors at the end of the Exposition, having since been cut up into singles and blocks Since only one sheet of each stamp was printed in each color/color combination, every individual Atlanta Proof -- that is, each plate position in each distinct color -- is necessarily unique.

Below, right, is a "normal" cardboard proof of #122 for comparison with the Atlanta. Note the orange and black position dots in the Atlanta proof, visible in the lower right corner.