Charles Heckel , Dec 01, 2008; 04:17 p.m.
Dark skin shouldn't make much difference in itself--in mixed group shots you want darker complexions closer to the light, and washed-out Nordics further from it. There may be enough range of complexion in the family that you will need to provide for it. A second consideration is lighting ratio--reflective skin handles a greater lighting ratio without losing detail in the shadows, and you may prefer 3:1 or 2:1 for darker skin.
Contrariwise, darker skin seems to pick up less of the hues of saturated colors, enabling dark-complected people to wear quite bright colors without looking cyanotic, jaundiced, or rosaceate. If you don't discuss the issue of coordinating or subduing colors to keep attention on the faces ahead of time, you may be faced with quite a melange at the shoot.