Growing up in Indiana, I and everyone I knew referred to bell peppers as "mangoes". My maternal grandparents were from Ohio and Wisconsin, and they called bell peppers "mangoes", as well. I asked my father-in-law, also from Ohio and in his seventies at the time, and he confirmed the usage in his day.
For years, people whom I have met (and, in at least one case, married) have thought I was crazy or making it up. Now comes proof from the interwebs that there is a quasi-logical reason for this semantic mix-up.
http://www.word-detective.com/2009/04/mango/