White light is comprised of all of the colours of the rainbow i.e. the light spectrum. Different materials absorb and reflect the different colours of light. The different colours represent different wavelengths of light.
A red object is only 'red' when you see the red wavelength of light being reflected off it. So a red car reflects red light, while the other light wavelengths get absorbed. The green light from your torch does not have a red wavelength in it. Because the red car only absorbs green light, no light is reflected and you are left seeing a black car.
Find out more on light through the external linkMuseum Victoria.
