1 Colour 3 what makes a colour ?

A simple colour. Filling the frame and exposing 5 different exposures from dark to light . I remember making a grey scale like this. !  exposure as :

Middle 5.6  stating F 4 f4.5 f5.6 F6.3 F8

The higher the number the darker the image . Lighter the lower more open the aperture.
the colour become richer under exposed but when taken further loses contrast .