Colour is a sensation. While wavelength can be measured with a spectrometer consisting of dispersive elements and colour insensitive detectors, detection of colour is accomplished by the eye, equipped with a lens, colour sensitive detectors, and a powerful processor in the form of brain. Sometimes this process results in unexpected phenomena. Different theories of colour vision have been proposed, such as the retinex theory of Land. In this lecture, we shall explore the land of colour vision.