All shark teeth are perfectly white when fresh (sharks don't smoke). Only when they fossilize and absorb some of the minerals from the surrounding matrix do they turn reddish, grey or black. Some colors are rarer, and collectors may prefer these colors simply for their rarity, or for their aesthetic appeal. It may be possible to relate the colors at Brownie's to the different layers of clay and sand in the Calvert formation. However, people have reported large variations in colors in fossil teeth or bones found right next to each other.
The only case in which I find color helpful at Brownie's is when I find a really pitch black tooth. Most of the time, these black teeth are much older Eocene teeth that have been reworked in the Miocene, or have washed in more recently from elsewhere.