About how many colours are usually named in a rainbow, and what is the underlying distribution?

1. About six colours are usually named in a rainbow: red, orange, yellow, green, blue and violet, with indigo sometimes added. 2. The eye tends to report only one of those names when it receives pure wavelength light. 3. Underneath the naming, the rainbow is a continuous distribution of colours according to wavelength. 4. The named bands are a convenience of language, not sharp physical divisions in the spread of wavelengths. _Source: OpenStax College Physics (CC BY 4.0), Ch 25 "Geometric Optics", section 25.5 Dispersion: The Rainbow and Prisms_