Interestingly enough, it has been known for some time on Roundworld that a small but significant number of people genuinely can see further into the ultra-violet than the rest of us. Such people were used in wartime to analyse intelligence photos, or as front-line scout troops, as they could identify artificial camoflage and tell it apart from natural plant growth around it - even where people with normal visual ability were fooled. The people gifted with extra colour vision would see factory-created artificial foliage glowing a sort of greeny-blue-purple colour, where the rest of us would just see green. Therefore they could tell EXACTLY where the Germans were hiding their tanks/artillery et c, and direct a barrage or air strike accordingly.
Effectively, people who are capable of seeing an extra colour exist now, but are hampered by frames of reference and semantics when trying to describe it. One draws an analogy with the way red shades into orange and clearly has a relationship to it. This is a colour which is as closely related to violet as orange is to red... and yes, apparently Colour X does have a greeny-purply quality to it...
It would appear that colour vision is something which is evolving fairly quickly in the human race. As sight is our dominant sense, this is only to be expected. Let us consider the indirect evidence to be gleaned from the earliest human writings, as clues as to how people perceived colour three or four thousand years ago. In Homer's Iliad, believed to have been written a little over three thousand years ago, there is an intriguing reference to a rainbow only having four colours; contextual evidence suggests the Achaeans saw only red, yellow, green and blue, and many had dificulties with the concept of purple. (strong wine is dscribed as either red or blue in colour, for instance) Today most people see six colours: others will add the elusive seventh, indigo.
This suggests that in three thousand years, the human eye has become a more sophisticated and refined instrument, capable of perceiving subtle nuances and gradations which our ancestors could not. And if today we're still stretching the envelope and some people today may see an eighth colour in the rainbow, what will colour vision be like in another three thousand years? AgProv 30 Nov 2008
But purple has been the imperial or royal color since classical times. Wikipedia suggests since the Minoan culture more than 3500 years ago. Today we have many names for various hues and shades of purple, but most people just call them "purple" (including violet.) I wonder how many colors the ancients saw that they just hadn't settled on names for yet. AgProv points out the elusiveness of indigo, which many will call either blue or purple and few will say where blue ends or purple begins. My wife calls any hue that isn't citrus orange or baby pink "red"; she seems unable to distinguish the salmon-pink of my sweater from a fire engine. Colors are as indescribable in language as musical timbres and as subjectively assessed; I suspect the ancients had the same ability to perceive them and the same difficulty describing them as we do. --Old Dickens 20:07, 30 November 2008 (UTC)