Just take a quick glance around you and you cannot fail to see a great many colours. But how is it that we actually sense these colours? Lets consider an apple as an example.

If it is completely dark, the apple will have no colour. And even if there is light present, we will not be able to see the colour of the apple if we keep our eyes closed. Finally, if the apple itself is not present, there is no colour. Therefore, we can see that three elements must be present in order for us to see colours: "a light source", "our sense of sight", and "an object". But why do we perceive colours as different? Why are an apple red and a lemon yellow? Also, in what ways are we conscious of the colours we see?