Genesis 30:40

And Jacob did separate the lambs, and set the faces of the flocks toward the ring-straked and all the brown in the flock of Laban; and he put his own flocks by themselves, and put them not unto Laban's cattle. By this second device the black goats and the white sheep were always kept by themselves, nothing in their own herd exciting their attention, whereas the herds of spotted and speckled animals in plain view were bound to make an impression upon the animals at the time of breeding.