A small correction-for the class of 2018 (the latest class for which information is available for all 3 schools) Bates had the highest percentage of kids from public schools (56%), Bowdoin was next (52%), then Colby (48%).
http://www.bates.edu/admission/student-profile/
http://www.bowdoin.edu/admissions/
https://www.colby.edu/admission/why-colby/profile/stats/