

Well, you can certainly see the difference in Sammy Sosa before and after. To teh left there you can see Sammy Sosa before: darkskinned. To the right there you can see Sammy Sosa after: lightskinned.
No, it doesn't seem to be a case of Vitiligo, like Michael Jackson had. That simply doesn't happen so evenly.
Sammy Sosa's description of the before and after is simply that he's been using a cream to soften his skin and that this has led, as a side effect, to its lightening.
For we can certainly see from those two photos with his wife to use as a contrast, that there has indeed been a change in Sammy Sosa's skin colour before and after.