For portraits where there is a lot of play in lighting, I generally prefer a black and white rendering. Where there's soft even lighting, I generally find that colour will work better. Of course with any of this, it's in the eye of the beholder.
Very directed lighting in this shot with a lot of fall off; high contrast. Shot with window light, Leica M9 w/50 Summilux
And this shot, with incandescent lighting. Very soft, low contrast front lighting. Nikon D800E w/Nikkor 85 1.4G