During the second season of Star Trek, Bill Shatner's toupee was noticeably lighter than his own brown hair, resulting in an easily detectable mismatch. Toupologists are often fascinated to see where real and fake meet in the world of Shatner's hair. This particular mismatch makes that quest very easy. We can see that the toupee actually reaches slightly down to the sides of the hair in order to blend in better, rather than being attached at the natural hair parting, which would be far more awkward. Here are some images from the episode "The Immunity Syndrome":
If we enhance (thanks to NASA scientists - not really) the above images, the mismatch is even more pronounced:
Conversely, if we color-correct the toupee, we see a match far closer to Shatner's own hair.
By the third season, this disparity was fixed and Shatner's toupee was made darker and thus closer to his real hair.
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