The Klingon makeup also varied throughout TOS. Neither Kras ("Friday's Child") nor any of the Klingons in "The Trouble with Tribbles" had darkened skin or bushy eyebrows. They appeared completely human, in fact, with the exception of costume.The Klingon makeup design has changed three times in ST history. It changed in TMP, where they went from racist Fu Manchu caricatures to guys with narrow, boney ridges down the center of their foreheads. It changed again in TSFS, when they suddenly had all sorts of bumps all over their foreheads. Worf's makeup design changed throughout TNG -- his bumps were totally different in "Encounter at Farpoint" vs "All Good Things," and the "All Good Things" flashback scenes kept the S7-era makeup!
https://memory-alpha.fandom.com/wiki/Kras
https://memory-alpha.fandom.com/wiki/Koloth
https://memory-alpha.fandom.com/wiki/Korax
Kor, Krell, Kang, and the captain in "Elaan of Troyius" are noticeably different from the above Klingons.
https://memory-alpha.fandom.com/wiki/Kor
https://memory-alpha.fandom.com/wiki/Krell_(23rd_century)
https://memory-alpha.fandom.com/wiki/Kang
https://memory-alpha.fandom.com/wiki/Unnamed_Klingon_military_personnel_(23rd_century)#Captain_001