Once upon a time, Zwolle found itself in the mortifyingly awkward and thoroughly un-Dutch position of being cash-strapped. Their only recourse was to sell their beautiful church bells to the nearby (and rival) town of Kampen... and then the haggling began. Many days, words and curses later, a deal was arrived at: Kampen would purchase the bells at a steep price, but would be able to decide what the method of payment would be.
The payment arrived soon after, in wagonfulls of pennies! Zwolle was thoroughly humiliated, disgusted and (predictably) suspicious. They counted every last penny. The copper oxide from the pennies made their hands blue, hence the name "Blauwvinger."
Truly an honourable heritage ;)