When the original Star Trek television series started, male and female officers wore similar outfits. The male Star Trek uniforms consisted of black pants, black boots and a velour shirt with the symbol on the left side.
Females wore the same type of shirt, with black boots and tights, and a black skirt, although in some cases they wore black pants.
The color of shirt worn identified the branch the crew member belonged to. Those in green shirts worked for command personnel, while beige stood for operations, and blue was for medical personnel only.
The velour shirts were changed to nylon shirts starting in the third season.
(infographic courtesy by: Costume SuperCenter)