Here's what my dermatologist and my cancer-man told me about the white spots:

The white spots on your skin are areas where one or more of your melanocytes (the cells that produce the "tan" of your skin and that can run amuck and become malignant melanoma) started going awry. So your immune system did its job and killed those suckers and any others in the neighborhood for good measure.

Now that white patch has NO protection from sunlight, and no hope of ever producing "tan" to protect itself. The melanocytes there are gone, gone, gone.

It's not a sign of something bad (actually, it's something good, your immune system killed rogue cells like it should). But you need to be sure to protect those white spots from sunlight. Sunblock or blocking fabric or umbrellas or whatever suits you.

Folks with white spots are more likely to have precancerous lesions, simply because they've had rogue cells before so have a statistical probability to deal with. Don't sweat it too much, but if you find a funny mole AND you have white spots already, take that funny mole seriously.

And wear your sunblock!