Matthew Poole and continuators on Genesis 30:40

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 flock by themselves; and put them not unto Labans cattle .

Such as were ring-straked and brown, from the white, as it here follows.

He caused them to go foremost, and the white to follow them, that by the continued beholding of them in the time of their conjunction they might have their colour more imprinted upon their fancies and thereby convey it to their young ones.

Which he did upon the same reason, lest the constant beholding of them should make them bring forth the like, i. e. single coloured ones.