People have wondered about the nature of light and color since ancient times.
Some people thought that light came from the eye rather than coming into the eye.
To see, light was projected（投射）from our eyes to illuminate things as we look at them.
Now we know that what we see is mostly reflected light, like the light from the moon which is reflected sunlight.
Light comes from a light source, such as the Sun, and either enters our eyes directly or after it has reflected off something.
In 1666 Sir isaac Newton showed that when light passes through a prism, it separates into all the other colors.
This clearly demonstrated that light is composed of many different colors.
The difference between colors is due to their wavelength.
A prism separates light into different colors because each color has a different wavelength.
The angle at which a color bends in a prism depends on its wavelength.
Colors with shorter wavelengths bend more than colors with longer wavelengths.
This explains why red light bends less than yellow light.
The reason is because its wavelength is longer.
Of the visible colors, violet light has the shortest wavelength, so it bends the most.
（A prism separates light into its component colors.）
（Each color is a single wavelength of light.）
If you have ever painted, you know that different colors can be combined to create new colors.
For example, if you add white to a color, you lighten it.
However, the three primary colors, red, blue and yellow cannot be made by mixing other colors.
It isn't possible to mix any combination of colors to create red, blue or yellow.
Mixing two primary colors creates a secondary color such as purple, which is made by mixing blue and red.
Mixing three primary colors creates a tertiary color such as brown or gray.
