QUESTION:
Have you ever tried to use a different colored filter other then
red, green or blue?  and would it give us different information?

ANSWER from David Soderblom on May 6, 1996:
The amount of light from an object at different wavelengths provides vital
information on how that light was created and was has happened to it since.
The best way to analyze the distribution of light with wavelength is to
pass the light through a spectrograph; this disperses the light by color,
making it possible to see details in the spectrum.  These details reveal
what elements may be in a star and how much of them, how hot a star is,
the kinds of stars making up the core of a galaxy (for example), and so on.

For very faint objects (distant galaxies, for instance), there isn't enough
light to be able to use a spectrograph, so we use a crude approximation:
pictures through filters.  If we can take, say, pictures through blue,
yellow, and red filters, we can get an idea of where most of the energy
is coming from and what the sources might be.

The filters we use in astronomy aren't just colored glass, they are
specially manufactured to high tolerance to have specific characteristics.
There are a few filters that are very frequently used, but there are
also many specialized filters.  Some of these isolate very narrow bands
of wavelength, making it possible to get a "spectrum" in a rough sense.
For example, gaseous nebulae often emit light of specific wavelengths
from hydrogen and oxygen atoms, but not at other wavelengths.  Filters for
those specific wavelengths make it possible to see the object as though
you'd obtained a spectrum of the whole thing at once.

Other filters allow us to measure how much iron is in stars without having
to take the time to get a detailed spectrum; this makes observing more
efficient.  Still others are tailored to other specific problems.

There are maybe a dozen "standard" filters that are heavily used in
ground-based observing and in HST, but there are dozens more used for
particular purposes.