Umm its just an observation that newton s ROYGBIV spectrum is different to ROYGCBV which is how I see the spectrum and how it is described in wikipedia I have read I think in a book called the last sorceror about newton s alchemical investigations a theory that there is no obvious colour between blue and violet so they speculated that newton included indigo just to make the list up to seven colours for mystical reasons There is a colour between green and blue and that colour is technically called cyan but I think most people would call it blue in a non technical context so there are in a sense two blues in the spectrum It is my own suggestion that newton was distinguishing between these same two colours and he called them blue and indigo ROYGBIV is still the most common description of the spectrum but I think it is just copying Newton s terms and doesn t actually match what most people see what do you see I was hoping someone might know a bit more and fill in the details Sorry I haven t signed in yet