Complex sentence: Uniforms at that time were violet áo dài, symbolising the purity of Vietnamese women, for which the school had also been called Áo Tím (Violet Dress) all-girls school.
Split into simpler sentences: Uniforms at that time were violet áo dài, symbolising the purity of Vietnamese women. For this reason the school had also been called Áo Tím (Violet Dress) all-girls school.