AFAICT ls uses the environment variable $LS_COLORS to define what colours are associated with which extensions. So if you re-declare that in your shell rc file (~/.(?:ba|t?c|z|k|pdk)shrc) you can pick and choose the colors of your choice e.g

export LS_COLORS=*.txt:01;32:*.pl:01;35:
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ls should now list *.txt files in green and *.pl in a purpley colour. The numbers and punctuation are in a standard escape code format, and generally go - \d\d(?:;\d\d;)?(?:\d\d)?. I'm not sure how portable this all is but I get the feeling that it should be applicable on most Linux systems.
HTH

broquaint