Italian Do-It-Yourself Virginity Test Kit

Mario is planning to marry and asks his family doctor how he could tell if his bride-to-be is still a virgin.
His doctor says, “Mario, all the Italian men I know use three things for what we call a Do-It-Yourself Virginity Test Kit. A small can of red paint, a small can of blue paint and a shovel.”
Mario asks, “And what do I do with these things, doc?”
The doctor replies, “Before you climb into bed on your wedding night, you paint one of your balls red and the other ball blue. If she says, ‘That's the strangest pair of balls I've ever seen', you hit her with the shovel.'