At least here in the western U.S., flocks of sheep used to contain 1 black sheep per 100 head to help determine the number in the flock quickly. Since that time, around 50 years ago, other methods have made numbering the flock more efficient. Although we are on a cow ranch, I've friends (I don't admit it very often) that raise sheep by the thousands. Having spent a great deal of time in the saddle observing these stupid, smelly creatures, it's doubtful they would know enough to treat a black sheep any differently...
Although most sheep raised near here are Rambouillet or one of its American bred cousins, the Targhee or Columbia, by breed, many do raise a black faced/footed sheep bred more for meat than wool, called Suffolk... not any smarter, though...