Today, and apparently back then also, the dominant color of Bedouin sheep is solid white and the dominant color Bedouin goats is dark brown or black. Spotted animals are in the minority and these are what Jacob proposed as his wages.
Moreover, he proposed to take only those that would be born thereafter and only those that would be born normally colored goats and sheep. This is why Laban removed that speckled animals from the others and place them in a three days journey away.
He may not have known much about genetics at that time, but he knew that speckled animals tend to give birth to speckled animals and solid colored animals tend to give birth to solid colored animals. Yet it was Jacob who proposed and welcomed this apparently disadvantageous arrangement, and he did so because he had faith in God.
His faith that God was going to bless him in spite of the cards not being stacked in his favor, and that he had been around animals for a long time and he knew that solid colored parents do sometimes give birth to speckled offspring, he felt very comfortable in making this agreement.
