Brown & whites
It is important to realize the standard in all of this. These color combinations are "undesirable". Anyone breeding away from the standard is not bettering the breed.
Some may ask why, why not breed multicolors, what difference would it make? The answer rests with those people, years ago, who intuitively understood genetics, and created the standards. The black color is the dominate color gene, while the other colors are recessives. The movement away from the dominant genes, lessens the attributes greatly "cherished" in the breed; basically the defining character of the breed.
The first generation a brown and white Newf may display the characteristics of the breed: massive bone, correct proportions, ie height gained from depth of chest, not length of leg, lovely temperament, etc.
The next generation one will notice a Newf that resembles a setter, and the generation after, the Newf will no longer display enough characteristics to be considered a Newf at all.
The breeding will become "watered" down, thus the term "Undesirable".
The breeding of quality browns and Landseers is much more challenging than that of breeding blacks, due to the influence of the recessive genes.
A breeder must be quite skilled, with great knowledge of pedigrees, and genetics to produce a quality Newf, and even more so, a Landseer or brown. When even more colors are added to the genetic color gene pool, the ability to produce quality Newfs is almost impossible. This is true of any dog; check the standards - there are always disqualifying colors, for this reason.