Jamieson, Fausset and Brown on Genesis 30:32

32. I will pass through all thy flock to-day--Eastern sheep being generally white, the goats black, and spotted or speckled ones comparatively few and rare, Jacob proposed to remove all existing ones of that description from the flock, and to be content with what might appear at the next lambing time. The proposal seemed so much in favor of Laban, that he at once agreed to it. But Jacob has been accused of taking advantage of his uncle, and though it is difficult to exculpate him from practising some degree of dissimulation, he was only availing himself of the results of his great skill and experience in the breeding of cattle. But it is evident from the next chapter (Ge 31:5-13) that there was something miraculous and that the means he had employed had been suggested by a divine intimation.