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https://www.mysticstamp.com/Product.../67__95/USA/ Quote:
Although these stamps may appear similar at first glance, they're all quite different. The most obvious difference is their color. The first stamp in the set – US #67 – was originally issued in a pale yellow-brown color. However, because the color of the stamp was so light, cancels showed up too heavily. Collectors protested and the stamp was reissued the following year in red brown (US #75). Then, the 5¢ Jefferson was discovered in brown (US #76).
Finally, the introduction of grills in 1876 resulted in another version of the 5¢ Jefferson, US #95. This last stamp in the series was issued with an F Grill.