depends on the purpose of your site. if you are interesting in doing shoots professionally, people typically shop by color or black and white. if you are putting them up for display, grouping them by person or mood or style would do wonderfully.
my vote: one area for color, one for b&w. in each you can visually categorize them by your choice: person, mood, technique, etc...
i say this because, psychologically speaking, each person responds differently to color and black and white. different responses lead to different tastes and desires. i have a research doc on that here somewhere....i'll try to dig it up.