Star Trek TOS 3rd Season Command Tunic (fabricated from a nylon diamond weave double knit fabric ), re-use for Phase II.

Worn by actress Persis Khambatta, as Ilia, for a wardrobe test.

 

See Phase II page for full description

star trek TOS screen used command dress 3rd season

This kind of dress doesn't appear frequently in the 3rd season. So far in following episodes :

That Which Survives (s3e17)
That Which Survives (s3e17)
The Lights of Zetar (s3e18)
The Lights of Zetar (s3e18)
The Way to Eden (s3e20)
The Way to Eden (s3e20)
Requiem for Mathusela (s3e21)
Requiem for Mathusela (s3e21)