First, if you get a lamb of a particular gender three times in a row, you'll get a lamb of the opposite gender, guaranteed. The rest is up to chance.
Second, any possible patterns are determined by the father alone. A lamb can inherent the pattern of the ram or none at all.
Third, the colors of the body and potential pattern are determined by the colors of both of the parents, which can be deviated somewhat from that color base for variety.
In the example below, using Brutus the Ram and a Brown Sheep produced the following different color patterns and sheep: