Genes come in matching pairs. If you get B from your father, and b from your mother, you will have brown eyes. If your father has B and your mother also has B , you will also have brown eyes. If you get b from your father and b from your mother, there are no instructions for melanin, so you will have blue or non-brown eyes. Now to get a little more complicated.
Skin color is determined by at least two sets of genes.
People with the darkest skin would have genes AABB and those with very light skin would have genes aabb . If the father passes on ab , and the mother Ab , then the child would have Aabb , or light skin. If the father passes on AB , and the mother passes on aB , the child would be AaBB , or dark brown. As you can see, all the skin colors in the world can come from just two medium skinned parents in just one generation. Probably medium skinned.