I spotted something on Wikipedia, and thought I might ‘bookmark’ it here for future reference.
Here we have an optical spectrum, in rainbow form, with the relevant wavelengths marked on. If I’m reading this correctly, the intervals are nanometres (1 nm = 1 billionth of a metre). This would be about right, as most sources quote the human visual range as something like 380nm – 750nm, or thereabouts.
(Image source: here.)
Interesting that people insist on calling the Sun a ‘yellow’ star (it’s not – sunlight is white light by definition). And particularly interesting in that, if you look at the above, you can see quite clearly that the Sun’s peak wavelength – 550 nanometres – is firmly in the green, not the yellow!