The times I've seen it turn colors was due to lack of proper follow up. In area's that have been neglected it will absorb whatever the contaminate is, say rust, oil, etc.
A good buffing and wax seems to make a protective coating over it, slowing or even stopping infiltration.
As with any repairs, the trick is to catch the damage as early as possible.
__________________
'75 Cuddy with '00 Johnson Ocean Pro 150 horse
Benny
|