"As a general rule most people just don't like a milky looking Silver Coin. Toning is one thing, but those dark spots or a Milky finish just doesn't make for a good seller."
I agree with Just Carl. I purchased a one ounce silver coin with some "milky" corrosion spread out along the bottom of the obverse. It threw me off quite a bit, so I sold it for its bullion value and got a BU American eagle for the same price.