^That's a shadow. The sides, and down onto his chin are fake. That directly under his nose is real. It can be seen in every role he played, from the sixties into the early nineties, including on 'Voyage to the Bottom of the Sea' and as the second Kane on 'Buck Rogers in the 25th Century'.
Well that getup from "Day of the Dove" is very fake, Christopher and I have pointed out how you can tell. Here's another angle, it's clearly a hair appliance.
Also, if you go look at PR photos of Ansara from the mid-to-late '60 he generally didn't have a mustache.
He doesn't have one in The Outer Limits episode he did a few years before "Day of the Dove" either, nor did he in the Lost in Space episode he did.
It's something he seems to have grown in the '70s, which would fit with Buck Rogers BTW.