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But wait, it's the penny black, not the penny red
Essentially, they are the same stamp. The red cancellation on the black stamp was unsatisfactory and the later black cancellation on the black stamp was not distinctive enough. So, the colour of the ink to print the stamp was changed from black to red.
Many of the "black" plates were used to print both Penny Blacks and then Penny Reds. Plate 11 was a Penny Red plate used for an emergency printing of the Penny Black. Thereafter, it, again, was used to print the Penny Red.
I doubt it is the only stamp in existence that was printed in more than one colour from a plate. Many countries used key plates to do something similar, using one plate for several stamps and a second plate for the value and / or the country name.