In the stage production the Usherette has traditionally been performed by the same actress as Magenta. In the original 1973 cast Patricia Quinn wore a pink usherette dress with an enormous Elvis Presley pin and carried a "Strawberry time" serving tray. The outfit was topped off with a fan-shaped cap (?) that read Sloane Cinema. The Royal Court Theatre (located in Sloane Square, London) was built in 1888, and for a period between 1935 to 1940 was actually used as a cinema before being closed from bomb damage in the war. The theatre reopened in 1952 and the smaller Theatre Upstairs (with just 63 seats) was added in 1969 - where Rocky Horror would premier 4 years later.


The dress has a straight yoke across the front, with a pleated segment (presumably ending in a waist seam). Often when a shirt or dress has a yoke in front it will have one in the back as well. It looks like there are pockets. It has a plain collar (with no collar stand) much like her maid dress in the film.
During the 60s and 70s Lyons Maid "Strawberry Time" and other frozen treats were peddled at theatres (film and stage). You can even find some of their previews/commercials from the 60s and 70s on YouTube - I grabbed a couple relevant screenshots below.

