are some OE calipers silver?

[Boxtaboy]

The base models came with black anodized calipers, but in many cases, putting them through car washes that use acidic wheel cleaners strips them of the black, and so they start looking so bad that the dealers end up stripping all the black off until the bare aluminum is showing. You can repaint them yourself if you want.

Now Porsche did once paint the calipers of the 911 C4 4 wheel drive models to signify the 4 wheel drive model range, but that does not apply to the Boxster line.