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In article <162300002@uiucdcsb> kadie@uiucdcsb.cs.uiuc.edu writes:

>I've got two miscellaneous science questions. 

>1) On TV's and computers screens, why is it RGB (red, green, blue)
>instead of RYB (red, yellow, blue) the primary colors?

>2) Some light wave length produces the color green. A mixture of
>the wave lengths of blue and yellow also produces green.
>Even though these two greens are indistinguishable to our eyes, are there
>(could there be) instruments that distinguish them?

(1)
You're talking about two different media here.  A TV monitor produces color
by mixing red, green, and blue light together in varying proportions.  This
is called additive color because you start out with black (no light) and add
light to make color.  On the other hand, when you produce color by mixing
paints, it is called subtractive color because you start out with white (all
colors) and remove light to make color.  For example, red paint absorbes all
colors except red so that when you shine a white light on it, it reflects the
red component and absorbes the rest.  If you shine a blue light on it, it looks
black because there is no red component to reflect.  It simply absorbes all the
blue light and reflects nothing.  Since subtractive systems work differently,
they need different primary colors than those used in additive systems.  For
example, color ink jet printers use primary colors of magenta (reddish),
yellow, and cyan (bluish).

(2)
Be careful, you are talking about subtractive colors, so to say you are mixing
blue and yellow wavelengths to produce green is not correct (see (1)).  Let's
try a different example.  If you mix red light with green light (as in a CRT)
you get yellow.  If you look at this light spectrally (e.g., using a prism),
you will see a peak in the red wavelengths and another in the green.  But it
looks yellow to our eyes because our eyes are fooled (don't ask me why our
eyes do this).  In other words, the mixture of two light frequencies causes our
eyes to perceive a new frequency (yellow).  Consider us lucky our eyes do this,
because otherwise color TV would have been impossible (or at least terribly
difficult).
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