I always thought of purple as the main secondary colour between red and blue – with violet, mauve and lilac being tertiary shades of purple. But Wikipedia suggests violet is the main colour, pointing out it’s the official spectral colour defined by its own wavelength. This makes sense, as ROYGBIV and ultraviolet sound better than ROYGBIP and ultrapurple (except perhaps in comedic uses).
Wikipedia also states that the Oxford English Dictionary defines purple as merely a ‘shade between crimson and violet’. Yet according to the Oxford Dictionaries website, purple is ‘a colour intermediate between red and blue’ with violet being simply ‘a herbaceous plant of temperate regions’. Oh, or ‘a bluish-purple colour’. So Wikipedia appears to have a pro-violet bias. There’s a sentence I didn’t expect to be typing.
Then again, Wikipedia’s violet page agrees it’s a tertiary colour, so maybe I have an anti-Wikipedia bias.