Great question! Letís first take a look at how colored *light* combines. (This is a little different from stuff like colored paint mixing together; weíll examine that later on.) When you turn off all the lights in your room, all you can see is black right? That means that black is an absence of all light, i.e. it contains none of the colors. Therefore you can guess that white light is a mixture of all the colors, and this is in fact correct. You can prove this to yourself by shining a flashlight through a prism:
A prism is a kind of lens that bends different colors of light by different amounts. When you shine white light through a prism, all the components of white light (red, orange, yellow, etc) get bent by different amounts. In other words, the colors that make up white light get separated out so that you can see them form a rainbow on the other side of the prism.
Now you might be wondering why, for example, colored paints donít do the same thing. After all, you can show very easily that if you mix colored paints together, you get a dark muddled mess instead of white. This is because the color you see from paint is the part of white light that gets reflected instead of absorbed. For example, when you shine light on blue paint, you see blue because the paint absorbs all of the light except for the part thatís blue, which is then reflected into your eyes. So when you mix a bunch of different colored paints together, you have all this stuff that absorbs most of the light that shines on it. For example, if you mix red and blue paint, the red light that is not absorbed by the red paint gets absorbed by the blue paint instead, and the blue light that is reflected by the blue paint gets absorbed by the red paint. If you keep
adding more paints to the mixture, pretty soon youíll get something fairly dark that doesnít have much color since the mixture absorbs so much light.
Hope that answers your question! For more information on light and optics, check out this great website: http://www.opticalres.com/kidoptx.html
(republished on 07/27/06)