QUESTION:
Does the Hubble have only red, green and blue filters?

ANSWER from Vicki Balzano on April 24, 1996:
  Two science instruments on-board the Space Telescope contain filter
wheels. The filters are used to select specific types of light for
examination by the science detectors.  For example, placing a "blue"
filter into the light path will only allow blue light to reach the
detector and be recorded. But, if you place a "red" filter into the light
path, then just red light will be recorded by the detector. By looking at 
the same object in different colors, astronomers can tell much about its
composition.
   The Wide Field/Planetary Camera has 48 different filters available for
use by astronomers. They range from the ultraviolet through the visible 
to the near infrared. (That is, from very short,very blue wavelength light 
to very long, very red wavelength light.) Although the human eye cannot detect
ultraviolet light or infrared light, we can see visible colored light.
So, the Wide Field/Planetary Camera has filters of every color: red, orange, 
yellow, green, blue, and purple.  
   The Faint Object Camera has 58 different filters and they range from
ultraviolet (very blue) filters to red filters. The majority of the filters
select specific types of ultraviolet light. So, although astronomers 
usually use the Faint Object Camera to detect and record ultraviolet light,
it does contains red, orange, yellow, green, blue and purple filters.