Amiee Williams, of Russell St School, asks :-

If black and white aren't colours what are they?

Rod Lambert, a physicist at Massey University, responded.

It all has to do with how we see what we see.

We "see" when light (from the sun or a light bulb) enters our eyes and strikes a special area in the back of the eyeball called the retina. This sends signals to our brain which then figures out what we are seeing. Sunlight is made up of all the colours that we can see and this appears "white" to us. Light from the sun (or anything else that glows) gets reflected off anything in the path of the light. But not all of the light is reflected. Some is absorbed. For example, a leaf is a green colour because it reflects the green from the sun's white light but absorbs the red and blue. (It needs light of these colours to help the plant grow.)

Now, imagine you are in a room with no windows and a closed door. You turn the light off. What would you see? I think that I would not see anything and would say that everything was black. So "black" is when no light gets into our eyes. Words printed in a newspaper are black because no light from the inked parts of the page gets into our eyes and we describe these parts as "black". So white is light with all of the colours mixed together and black is no light at all.