A wise man once observed that "All swans are white." is true if and only if "Things that are not white are not swans".
So one day, you see a green mini. That is a thing that is not white, and lo, it is not a swan.
So the green mini is evidence that things that are not white are not swans, and so it is evidence that all swans are white.
If you do not buy this argument, why do you believe that swans are white?