mixing colours science & art

[mollykins]

I know that light is made up of different colours and mixing them make more colours.

But why is it that the colours mix to make different colours in light than paint ect.

for example red and green light make yellow but with paint it makes brown.

WHY?

[mollykins]

I just looked and blue and red make magenta which is similar to if you mixed it with paint but blue and green make light blue, red and green make yellow and if you mix the magenta light blue and yellow you get white. Which definatly doesn't happen with paint.

[fo3nix]

It depends whether the colour is seen by illumination, or reflection from some other source.

Light contains the illumination, paint colour is seen with reflected light from some other source.

http://en.wikipedia.org/wiki/Additive_color

[gen2]

When you mix light, you are always adding to what you have already. Such mixing is 'Additive'. In an extreme case, mixing all colours give you white light.

Paints are pigments that do not emit their own light. You see them by reflected light. If the pigment absorbs some frequencies then the reflected light will be missing those frequencies (colours).
Mixing pigments means that you are not only absorbing (taking away) the characteristic frequencies of the first one, but also taking away the characteristic frequencies of the second one as well. What is left is the colour you see. This is the 'Subtractive' process. In the extreme case where you mix all pigments together, the mixture will absorb almost all frequencies and be close to black.

[mollykins]

thanks both of your answers were very useful.