Technically colour doesn't exist in the 'real world' as colour is a perception; the result of our brain interpreting the wavelength of light. In the 'real world' light waves have different wavelengths and our brains are equipped with the tools to interpret wavelengths that exist in 'visible light' to produce the percept of colour. Short wavelength light appears blue, medium wavelength green and long wavelength red. When those tools aren't present, our ability to perceive colour disappears. Humans have 'trichromatic vision', as our retinas contain three types of photoreceptor cells or cones - red, green and blue cones which allow us interpret these base colours. If a person is born without one of these cone types it results in 'colour blindness' (dichromatic vision) where they struggle distinguishing certain colours. If someone was born with only one cone type they would have monochromatic vision and only see the world in black and white, although this is extremely rare. However, there are cases of 'Cerebral Achromatopsia' where due to brain damage to a certain areas of the visual brain the world appears in black, white and grey.