"One of the intentions of the colours was to promote public awareness of the depth of the belief for suffrage in England. Women were encouraged to 'wear the colours' to show support for the movement and to stand out in the crowds during public demonstrations. They particularly wanted the men that were opposed to the movement, to be aware of the connection of the colours to the suffrage, in this they succeeded.

The characters on many anti-suffrage postcards drawn by male artists of that period were often draped in sashes and banners of purple white and green, presuming that a suffragette would be recognised by her colours, even by those who opposed the movement.
Source: https://preciousasapearl.com/blogs/news/suffragette-and-what-they-stood-for