It doesn't matter what color merle, how much merle the parents have, how little (or how much) white trim, what breed they are, or even that the parents are the same breed. (lethalwhites.com)
Because the Merle gene is dominant over other color genes breeding a Merle parent with a non Merle parent will statically guarantee at least one puppy in a little of four or more will be born with a Merle patterned coat. (pethelpful.com)
Due to the double merle or «lethal white» gene being passed on from two merle parents and leading to a very high chance of vision and hearing problems, be wary of buying a rare white Aussie. (vetbabble.com)