[redfox]

I'm making a coded letter for someone and need them to figure out the word 'Graham' as part of it. I've decided to start with telling them the wavelength of grey, but the problem is that I can't seem to find its wavelength in nm (which, I suppose, is because it's not a colour). Is it only a mix of colours? I know it's its own complement...so does that mean it won't appear on the spectrum?
If it doesn't...does anyone have any ideas of how else (in a similar manner - using chemistry/wavelength) I can lead to the colour please?
Ta!

[UG]

I think that when something absorbs almost all of the light, we see it's colour as black. When something absorbs most of the light, but reflects light of all wavelengths about equally, we see a colour between white and black: grey