I actually did notice that! I read some trivia about "Day of the Dove" saying that Kang's wife's make-up came off on Chekov and thought I should watch out for things like that from now on, and sure enough, it happened on this episode. In the scene where she was getting really 'friendly' with Kirk I knew it was bound to happen sooner or later, so I kept a close watch for it.
It just strengthened my conviction that they should have let Yvonne Craig just look like herself. That was the funniest unintentional moment after she kissed Kirk and you could clearly see the green on his hands. It must have taken some restraint for Shatner not to ruin the shot by not staring at it or trying to cover/wipe it off.