Color certainly makes a difference. Stay away from the lighter, dull colors. A gray strand, for example, should sell for much less than a dark strand with a green overtone or a rose overtone.
When pearl lots are auctioned off the highest bids always go to lots that have good orient, and peacock overtones. The next most valuable are the dark lots and the green lots. Lots of gray and light colored pearls, even clean, will sell for less than B/C peacock.
In a nice peacock strand you should be able to see a lot of different colors throughout the strand, and throughout the individual pearls. The strand does not necessarily need to be dark to be peacock. After every buy we are typically able to make one or two peacock strands with a more unique body color (like blue), but most are going to have a green bodycolor.