Custom message-cite-prefix-regexp

[giglio robbo' d'acciaio]

My value is "\\([       ]*[-_.[:word:]]+>+\\|[  ]*[]>|}:+]\\)+" as suggested
                                                       ^
in order to parse as quoting also rows starting with `:', but it doesn't work
correctly since it parse also `:'s in the middle of rows, (i.e. "http: ...").
Is it possible to enhance it?
-- 
      Daniele Giglio      Dona i tuoi cicli di clock alla ricerca!
      dgiglio@iol.it      http://boinc.berkeley.edu/
                          --------------------
             TASSISTA (1) - Esattore.

             TASSISTA (2) - Zoologo specializzato in tassi.