Shatner's hair is now a transplant. It looks like he colors his hair still, looking at pics from public appearances.
His denial of wearing a rug? At first, I'm sure it was out of vanity, but later became sort of a "nudge, nudge, wink, wink" thing. Surely he knew that the post-Jim Lace and the early version of the TJ Curly were obviously not his real hair. We who like The Shat just snickered along with him.
Robin Curtis tells a story about the scene in TSFS on Vulcan from her point of view standing behind Shatner, about the hair person combing and blending the back of the toupee into his own hair. And trying to be quiet.
Someone has suggested that DeForest Kelley wore a rug. I don't see it. I've read a story where he explained that when he was cast, GR sent him to Jay Sebring for a new ($35, in 1966 dollars!) hairstyle, and what I see in pics seems to be consistent with that. In his later years, Kelley's hair looked as natural as any I've ever seen. If that was a toupee, it was a good one.
But back to Shatner.
During the run of
Star Trek, his hair was thinning, but he wasn't anywhere near bald. He likely wore a "cap" to cover the bald spot on the back of his head with his real hair combed back over to hide the line, much like Ted Danson did in the
Cheers years.. Some pics look like there might have been a front piece with the lace glued down and covered by makeup, but the pics aren't conclusive as far as I'm concerned.
The legend of Shatner's Toupee will live on, likely for many generations after the man is gone.