This java applet let you play with mixing light beams and paint pigments.
Click on the ovals and drag them around. When they overlap you can see how the colours combine.
Click the right mouse button twice quickly to switch between two different modes:
Enter RGB values into the text field to change the color of the selected oval.
The color code (RGB value) at the mouse tip are shown in colored background.
Additive Color Model
Red , green and blue are
the additive primary colours. Combining (adding) all three additive primaries
gives white. Leaving just one of them out is like subtracting that colour from
white. For example adding red and green together gives yellow, the same result
is achieved by subtracting the blue from white light. This is the way light
mixes (try it with coloured light bulbs). The background is black as you start
with no colour (no light) so you can see what happens as you gradually add
colours.
The colours you get by overlapping the primary colours in pairs are the subtractive
primaries.
Subtractive Color Model
Yellow , cyan (light blue) and
magenta (purple) are the subtractive primary colours. The white background
is a mixture of the additive primaries red , green and blue. Each subtractive
primary removes just one of those colours; for example, yellow takes away all
the blue, leaving just red and green. And your eye perceives a mixture of red
and green as just one colour, yellow. You can think of the yellow circle of
colour as a filter sitting on the white background. The yellow filter absorbs
(subtracts) the blue and allows the red and green (which combine to give yellow)
to pass through. When the yellow, cyan and magenta filters are overlapped all
of the primary colours are blocked so no light from the white background reaches
the observer...that area is perceived as black.