Final answer:
Objects show specific colours due to their unique absorptive and reflective properties, wherein they absorb certain wavelengths of light and reflect others. The reflected light determines the color we see. The true colour of an object remains constant, even though it may appear different under coloured illumination.
Step-by-step explanation:
The two possible reasons for an object to show a particular color are its absorptive and reflective characteristics. When white light, which contains all colors of the spectrum (ROYGBV), falls upon an object, certain wavelengths are absorbed, and others are reflected. The reflected light is what we perceive as the colour of the object. Gray objects uniformly absorb light across the electromagnetic spectrum, while coloured objects have more complex behaviors for specific wavelengths, giving them their unique appearance. If illuminated by light of a different color, such as a blue object under red light, the object can appear black because it absorbs all of the red light. This demonstrates that the true color of an object is independent of the illumination.