Consistency in the use of colours by political parties is a relatively recent innovation, despite the obvious benefits that arise from it, as these examples from the Liberal Party at the 1970 general election show. Orange was the dominant party colour but it was by no means universal:
It wasn’t just the Liberals who mixed and matched colours as this Conservative Party poster demonstrates:
For more gems from past election leaflets, see my collection How leaflets used to look.
Thank you to the staff at the LSE Library for helping me locate these leaflets as part of my hunt for the first barchart.