Genesis 30:31

If thou wilt do this thing. When Laban repeated his offer, evincing his seriousness in making it, Jacob proposed terms on which he would be willing to stay. His proposal was based on the fact that in the Near East goats, as a rule, are black or dark brown, rarely white or spotted with white, and that sheep are for the most part white, seldom black or speckled. Inasmuch as Jacob’s proposal involved but a small part of Laban’s flocks and herds, Laban hastened to approve of the plan (v. 34). Jacob offered, furthermore, to begin separating them “that day,” so that Laban might be able to see just what the results were likely to be.

The further course of the narrative shows that more was involved in the agreement between Jacob and Laban. Either Moses chose to mention only the basic principle of the agreement, and so omitted the fact that the separation was to be repeated at regular intervals, or this point was not mentioned at first, but rather taken for granted by both parties. Either way, Jacob proceeded accordingly, to which even Laban, notwithstanding his frequent alterations in the contract, does not appear to have taken exception (ch. 31:7, 8, 41).