Koenig had a toupee at first, too, and Nichols and Whitney had wigs all througout TOS.
Also, Nimoy's ears were actually latex add-ons and the Talosian performers didn't really have big, throbbing brains. And I believe that each and every actor also wore (gasp) make-up! At least, I heard that at a convention once.
What??? Next you'll be telling me the pointy sideburns were fake and that there's no Santa.