Genesis 30:25-43

²⁵ And it came to pass, when Rachel had borne Joseph, that Jacob said to Laban, “Send me away, that I may go to my own place and to my country.

²⁶ Give me my wives and my children for whom I have served you, and let me go; for you know my service which I have done for you.”

²⁷ And Laban said to him, “Please stay, if I have found favor in your eyes, for I have learned by experience that the Lord has blessed me for your sake.”

²⁸ Then he said, “Name me your wages, and I will give it.”

²⁹ So Jacob said to him, “You know how I have served you and how your livestock has been with me.

³⁰ For what you had before I came was little, and it has increased to a great amount; the Lord has blessed you since my coming. And now, when shall I also provide for my own house?”

³¹ So he said, “What shall I give you?” And Jacob said, “You shall not give me anything. If you will do this thing for me, I will again feed and keep your flocks:

³² Let me pass through all your flock today, removing from there all the speckled and spotted sheep, and all the brown ones among the lambs, and the spotted and speckled among the goats; and these shall be my wages.

³³ So my righteousness will answer for me in time to come, when the subject of my wages comes before you: every one that is not speckled and spotted among the goats, and brown among the lambs, will be considered stolen, if it is with me.”

³⁴ And Laban said, “Oh, that it were according to your word!”

³⁵ So he removed that day the male goats that were speckled and spotted, all the female goats that were speckled and spotted, every one that had some white in it, and all the brown ones among the lambs, and gave them into the hand of his sons.

³⁶ Then he put three days’ journey between himself and Jacob, and Jacob fed the rest of Laban’s flocks.

³⁷ Now Jacob took for himself rods of green poplar and of the almond and chestnut trees, peeled white strips in them, and exposed the white which was in the rods.

³⁸ And the rods which he had peeled, he set before the flocks in the gutters, in the watering troughs where the flocks came to drink, so that they should conceive when they came to drink.

³⁹ So the flocks conceived before the rods, and the flocks brought forth streaked, speckled, and spotted.

⁴⁰ Then Jacob separated the lambs, and made the flocks face toward the streaked and all the brown in the flock of Laban; but he put his own flocks by themselves and did not put them with Laban’s flock.

⁴¹ And it came to pass, whenever the stronger livestock conceived, that Jacob placed the rods before the eyes of the livestock in the gutters, that they might conceive among the rods.

⁴² But when the flocks were feeble, he did not put them in; so the feebler were Laban’s and the stronger Jacob’s.

⁴³ Thus the man became exceedingly prosperous, and had large flocks, female and male servants, and camels and donkeys.

By this time, Jacob had more than fulfilled his contract with Laban. He was with Laban a total of twenty years altogether (Genesis 31:38), including the fourteen years he had served for Leah and Rachel. — Morris, page 470

Jacob went to Laban and announced his decision to return to his home. … Laban, however, was very reluctant to see him go. He had prospered greatly because of Jacob’s abilities and faithfulness, and he was willing to make almost any bargain that would keep him working for him. Laban even acknowledged that the Lord was with Jacob, and that it was of the Lord that he had profited so much through Jacob. …

The phrase “learned by experience” (v. 27) … represents the Hebrew word nachash, and means literally “learned by enchantments.” He [apparently] had in some way either carried out certain divination practices of his own, or else consulted some kind of soothsayer or oracle. — Morris, page 471.

Wechsler comments on Laban’s “enchantments.”

Though recognizing the fact that the Lord has blessed him, Laban’s affirmation is based not on personal faith in the sovereignty of the True God, but rather (in addition to simple observation of his material wealth) on divination, in which the reference is not merely to “discerning” something, as the English verb “to divine” is often used, but in fact to the pagan religious practice (e.g., “reading” livers, observing the flight of birds, etc.) that is elsewhere specifically condemned by God (cf. Leviticus 19:26; Deuteronomy 18:10; 2 Kings 17:17). Nonetheless, God’s promise of blessing for those who bless His covenant family is not dependent on the nature of one’s faith. — Wechsler, pages 234-235.

It was reasonable that Jacob, having fulfilled all his commitments to Laban, should begin to provide for his own family. Laban again, therefore, asked what he could give him to make him stay. Jacob did not wish Laban to “give” him anything. … Instead, he agreed to shepherd and supervise Laban’s flocks, exactly as he had been doing, and his pay would consist of those animals yet unborn that would be less desirable to Laban because of their markings. It would thus be entirely up to God as to how many animals would become Jacob’s. 

Only those future animals that would be born speckled or striped or spotted, or abnormally colored in some way, would become Jacob’s wages. The dominant color traits in Laban’s flocks and herds were evidently white among the sheep, black among the goats, and brown among the cattle. …

Jacob further proposed that, not only would none of the living speckled animals be taken by him, but they would not even be used fore breeding purposes. he woudl separate them into a separate flock, and keep them away from the normal-colored animals. Only such spotted and speckled animals as would be born in the future from the normal-colored animals would become his. … This arrangement clearly was highly favorable to Laban and of very doubtful value to Jacob. …

Laban … immediately jumped at the chance to seal such a bargain. He would lose nothing that now belonged to him, and it appeared very unlikely that Jacob would acquire any future animals by this process either.

Laban decided not to trust Jacob to keep the two sets of flocks separate. He himself, probably aided by his sons, went through the flocks, culling out all the striped and spotted goats, the brown sheep, and other odd-colored animals, and he put them into a separate flock. … Then, to make it quite impossible in the future for there to be any mixing, he gave the speckled flock into the hands of his sons, and told them always to keep them at least three days journey away from the main body of animals which would be tended by Jacob — Morris, pages 472-474.

Even though a species of animal may have certain “dominant” traits (such as the white color in this type of sheep), there are, in each generation, certain individual animals that manifest one or more “recessive” traits (such as the brown color among sheep). … Jacob believed that he could simply trust God to increase the statistical proportion of animals in future generations of Laban’s flocks that woudl appear with these recessive traits. …

Many commentators have suggested that Jacob deceived Laban by making this bargain, and that he used unfair means to increase the proportion of spotted and striped animals. It should not be forgotten, however, that Jacob was given the opportunity by Laban to set his own wages. … He made the bargain as difficult for himself, and as generous to Laban, as it could possibly have been. There is no basis at all for any criticism of Jacob’s conduct in this regard.

It may be that Jacob had learned certain things [about the transmission of hereditary factors] which modern biologists have not yet even approached. … It is surely very unlikely that an external image can be transmitted through the visual apparatus to the brain and thence in some way as a signal to the DNA structure to specify certain characteristics to be triggered in the embryo, [but] it is nevertheless true that certain chemicals can and do have a significant prenatal influence if they can reach the embryo or, prior to conception, the DNA in the germ cells. … If nothing else, water treated thus may have served as an aphrodisiac and fertility promoter among the cattle. At least one such chemical substance found in these threes has been used for such a purpose in both ancient and modern times. … This in fact seems indicated by v.38, in which the word translated “conceive” in the KJV is actually the Hebrew yacham, meaning “to be hot” [or “in heat”]. … Jacob wanted to speed up the reproduction process and to induce the animals to have as many offspring as possible in the shortest time possible. …

When the animals did conceive and bear, Jacob was possibly quite surprised to note that a larger proportion than he had expected were ring-streaked, speckled, and spotted. He placed these animals in a group by themselves, after they were weaned, no doubt, and thus had the beginning of a flock of his own. …

A further measure was taken by Jacob to ensure that the flocks so produced would be composed of strong animals. He divided the flocks into two shifts, composed of stronger and weaker animals, respectively. He used the rods in the troughs when the stronger animals drank, but not when the weaker ones came there. Thus the stronger animals were stimulated to mate, and the others were not. This measure, likewise, to the extent it would be effective, constituted a sound practice of animal husbandry, and should have been of as great benefit to Laban as to Jacob. It would ensure that, statistically at least, most of the newborn lambs and kids, whether solid color or spotted, would be sturdy and healthy. However, there continued to be produced an abnormally large proportion of spotted and speckled young. This meant that a greater and greater percentage of the animals in Jacob’s flock were strong animals, and an increasing percentage in Laban’s were weaker animals. 

It was not until later that Jacob came to understand the providential intervention that caused the unusual percentage of streaked and spotted animals to be born (see Genesis 32:10). In the meantime, within the space of only a few years … Jacob’s flock had grown so large, and he had prospered from it so greatly, that he had to employ many servants, both male and female, and had purchased many camels and asses. He had quickly become a very prosperous rancher. — Morris, pages 474-477.

Wechsler has a different take on Jacob’s handling of the flocks.

Jacob—still not trusting in the sufficiency of God’s covenant provision—continues his behavioral pattern of seeking to better his circumstances through his own machinations and maneuverings. It is in this connection that the elaborate process of intermittently setting up freshly peeled rods of poplar, almond, and plane trees should be understood—that is, to emphasize the degree of Jacob’s human striving to attain what God has otherwise promised to bestow in His own sovereign power and grace. — Wechsler, page 235.

I don’t know. The preponderance of commentaries treat Jacob as a schemer and, therefore, in the wrong. But in the absence of any Scriptural support for the view, I’m reserving judgment and inclining toward Morris’ viewpoint.