Patina is the Discworld Goddess of Wisdom. Classically she had an owl perched on her arm, but a sculptor with no ornithological knowledge carved a penguin on her statue. This image is now burned into the minds of Ankh-Morporkians.
The Three Penny Patina stamps were printed in sheets of 28 stamps. Appropriately for a stamp issued in the Year of the Backward-facing Artichoke the Sport stamp shows a forward-facing penguin.

The common (left) and the Sport (right)

Note: I saw a preview of this stamp and I am sure that the colour shaded vertically from a more blueish hue to the purple. If anyone else can confirm this please let me know.