Violet light: the traditional description of a rainbow is that it is made up of seven colours (R, O, Y, G, B, I and Violet - or purple). However, a rainbow is a display of a spectrum of wavelengths of light - recognised by us as colours - some of which the human eye does not see - yet.
A rainbow is not a thing in a specific location, it is an optical phenomenon which is dependent on the positon of the viewer – we each see a different rainbow which is actually a circle not an arc.
When light exits a water droplet (e.g. rain or mist) it bends and is separated into wavelengths.
Purple Perception is therefore symbolic of having the capacity to reach beyond the edge of what is seen and known.