This topic is being discussed on some other threads right now, but this is a better discussion, so I’m boosting it.
Related threads:
** http://boards.straightdope.com/sdmb/showthread.php?threadid=45763 How many colors can the human eye see?
http://boards.straightdope.com/sdmb/showthread.php?threadid=38714 How do we know what colors animals see? Are any creatures able to see more colors?
http://boards.straightdope.com/sdmb/showthread.php?threadid=33318 Colorblind animals?
http://boards.straightdope.com/sdmb/showthread.php?threadid=28171 Are horses color blind?
http://boards.straightdope.com/sdmb/showthread.php?threadid=15793 Cats colorblind or not?
http://boards.straightdope.com/sdmb/showthread.php?threadid=14470 Do all people see colors the same?