"During this prosperous period, it was customary for wealthy families to hire domestic servants to perform the day to day household duties. This was so common, in fact, that garment manufacturers advertised servants' uniforms in women's magazines of the period. Just as the lady of the house had certain types of clothing for certain times of the day, so too did her servants. In general, afternoon and evening uniforms were more formal in appearance than the morning uniforms.
"The maid's afternoon uniform consisted of a taffeta, crepe, moiré, or poplin dress in dark blue, green, brown, burgundy, or plum. Gray or black was preferred by the older, more 'conservative houses' or for evening affairs. The waistline for maids' uniforms remained primarily in its natural position. Matching white collar, cuffs, apron, and gathered or pleated headpiece were standard. The headpiece was worn over the area between the crown of the head and the forehead. It was tied in the back with an attached ribbon. For fancy afternoon or evening wear, these items might be made of lace."
From Fashions of the Roaring Twenties by Ellie Laubner. Schiffer Publishing LTD, USA, 1996.