Italian Do-It-Yourself Virginity Test Kit

Mario is planning to marry and asks his doctor how to tell if his bride-to-be is a virgin.     
His doctor says, "Mario,  Italian men I know use a can of red paint, a can of blue paint."
Mario asks, "So, what do I do with these things, Doc?     
The doctor replies, "Before you climb into bed on your wedding night, paint one of your balls red and the other blue.

You will know If she says, 'That's the strangest pair of balls I've ever seen!'.