BLACK or WHITE do not exist and are not colours but... colours.

In terms of wavelength (Newton's Prism) white and black are not colours, just like magenta, brown, pink, grey... But in terms of feeling and perception they are. We therefore use the term colour, reserving the term colour for the scale of luminosity.

As in nature, their composition is based on numerous colours that are revealed on dilution. Their mixtures give rise to subtle coloured greys.