Seems to be a lot of people typing
what colour is indigo
into google. Why all the fuss about indigo?
In case you are one of those people I can tell you that in the spectrum indigo was generally considered to be associated with wavelengths in the range 420nm – 450nm though many would argue that it is not in the spectrum at all and that light below about 450nm is considered to be violet. Have a look at my earlier post about why indigo is generally not considered to be in the spectrum by modern colour scientists.
In terms of RGB (sRGB for the techies) it can be approximated as R=75, G=0, B=130 and this looks like this:
Though of course, the RGB on-screen representation is not the same colour as the indigo in the colour spectrum since every colour in the spectrum is outside the gamut of your RGB display and therefore cannot be properly shown.
The word indigo is named after the blue colorant obtained from plant indigofera tinctoria.