Yep.
Amoringello's right.
You need to have the right kind of light for darker-skinned subjects.
Full sun lighting will just not do it for you, nor does it flatter any other kind of subject.
So, take your subject into the shade and eliminate any background highlights the sun produces and you may find a more balanced exposure.
Generally I still use centre or matrix metering (not spot) since I don't want the face to be overexposed and blow out anything else not dark in the frame. I have gotten good results in this regard with all cameras I've used, not just my K-5. An example with the K20D:
...but as you can see the clothing was still clipped in the highlights by virtue of the high contrast between the skin and the white apparel. The K-5 would have done a better job of this portrait, especially at ISO 80 or 100.