According to the IWD website, purple is a colour for symbolising women, signifying justice and dignity. The colour, along with green and white, was historically associated with The Women's Social and Political Union (WSPU); a women-only political movement and leading militant organisation campaigning for women's suffrage in the United Kingdom from 1903 to 1917.

The above image is taken from the V&A: It depicts the weekly newspaper of The Women’s Social and Political Union.