Extremely rarely, the undesirable allele combination e/e (E locus) appears in Collies and then covers the basic coloration and the nose with a reddish light brown color. The white remains on the collar, legs, etc., so that they are reminiscent of Sable Collies. If it covers Merle, they are also called Hidden Merles.Inheritance is recessive, i.e. the two rare genes must meet in both parents to produce this color. On the other hand, affected alleles can spread completely unnoticed as long as they are covered by a second, unaffected gene and no color changes occur. It is a common color variation in Setters and Retrievers and doesn't cause there any health problems. Some debate wether it has not always been present in Collies as well. Either way, it is considered undesirable today because it overlays everything else.

Maltese Blue, also called Maltese Gray, causes a dilution of all colors (eumelanin & pheomelanin). There have been known cases of matings between Classic Blue Merle and Tricolor. While most offsprings are normally colored Tricolor and Classic Blue Merle, there are some whose coats are medium to dark gray, with a tendency to darken as the animals grow. They are somewhat reminiscent of Collies with Atypical Merle. However, in the Maltese Blue, the originally tan markings also lighten to cream. The White on the collar, legs, etc., is normally developed. It should not be confused with GCS (see below).

Leigh Anne Clark et al. discovered in 2018 that an additional mutation at the D-locus (dilution) is present, with the expression d/d, which leads to this undesirable coloration. Inheritance is recessive, meaning the two rare genes must coincide in both parents to produce this color. On the other hand, affected alleles can spread completely unnoticed as long as they are covered by a second, unaffected gene and no color changes occur. According to Dr. Clark, no health problems are to be expected, which is also consistent with reports from owners (all outside our association). 

Maltese Blues should not be confused with Collies affected by Gray Collie Syndrome (GCS), also known as Cyclic Neutropenia, which results in a dramatic decrease in white blood cells (granulocytes) approximately every 11 days. They also have a grayish coat, but usually even lighter, lacking tan markings and lacking full pigmentation on the nasal surface. These dogs are usually in very poor general health, as they are very susceptible to infections. Therefore, they often lag significantly behind their healthy littermates in terms of development. Many do not reach adulthood but die from simple infections. Our breeding regulations prohibit the birth of such dogs. Test: https://labogen.com/en/genetic-diseases-dog/grey-collie-syndrome-canine-cyclic-neutropenia-gcs/ . Further detailed information is available in our breeding program for GCS:

GCS (Gray/Grey Collie Syndrome or Cyclic Neutropenia-CN): This is a rare genetic disease of blood cell formation in the bone marrow, which leads to a cyclical reduction, especially of neutrophil granulocytes, which are extremely important for the immune system. The latter are the main component of the cellular immune system. Their strong reduction every 11 (10-14) days means that affected dogs are very susceptible to infection. As long as puppies are still being suckled, the antibodies from the mother's milk still seem to have a supportive effect, and the environment is usually relatively germ-free. Until then, the most noticeable feature is the slightly lighter, usually grayish coat color (not caused by Merle), with a nose that does not completely turn black over the course of development, which also remains rosy at first and later grayish. In addition, the tan markings are missing. The greatest risk of symptoms developing is at 8-10 weeks. With few exceptions, a terrible ordeal then begins with infections that become increasingly severe and, sooner or later, life-threatening, initially often caused by the simplest pathogens, that have only little effect on healthy puppies and young dogs. The illnesses are often accompanied by recurring fever, diarrhea, sometimes vomiting, joint pain that soon develops into arthrosis, sometimes accompanied by misalignment. Respiratory infections that develop into serious, life-threatening pneumonia are also typical. The eyes, skin, mouth and teeths are also very susceptible to all kinds of pathogens. Since the entire blood formation is disrupted by the cyclical changes (hence also called cyclic hematopoiesis), anemia can easily develop, possibly accompanied by a blood clotting disorder and symptoms such as nosebleeds and omnipresent additional general weakness. The affected dogs usually die within the first three years of life. Reciprocal bone marrow transplants from sick dogs to healthy ones, which then became ill, and vice versa from healthy dogs to sick dogs that had a chance of recovery, have proven that the cause can clearly be found in the bone marrow. Unfortunately, there is no sufficient developed system for finding suitable bone marrow donors in dogs. There is a similar disease in humans, cyclic neutropenia (CyN). A mutation in exon 20 of the AP3B1 gene has now been identified (https://omia.org/OMIA000248/9615/ ). This primarily causes a deficiency in the enzyme elastase (including agglutination of the precursors that cannot be completed) and, as a result, a disruption in the movement and function of the granulocytes, up to the failure to trigger a final immune response to fight infections. The gene is also the cause of a form of coat dilution, that causes the eponymous gray coloring in affected animals. It can also vary to a beige-yellowish color, depending on the base color and as a new color variant after the rare coat change. The harsh structure is usually also missing. This mutation has now been found in distantly related breeds, and the search is still ongoing in other breeds. These matuations probably occurred very early in the evolutionary history of dogs. In all probability, both parents (carriers) already have limited granulocyte function. We are happy that a suitable genetic test has been developed. Everything suggests that our gene pool is also completely free of carriers and ideally stays that way. When our association was founded, we established the rule that at least one parent in every mating must be genetically free (GCS +/+ or N/N). In the meantime, every breeding candidate must be tested for GCS. This means that the birth of GCS-affected puppies has been and will continue to be completely prevented in our association AC e.V.!

Despite the brightening effect, fever coat has nothing to do with merle. A (usually harmless) infection during pregnancy can be a trigger. Excessive stress has also not been ruled out as a potential trigger. The key point seems to be when the puppies begin developing the pigments for their coat color. If a disruption occurs here, the head (sometimes extending to the shoulders and forelegs) is a normal strong colored, while the rest of the body's coat is more or less brightened. Often, it is only a slight shade. This effect is only temporary. During the next coat change (at the latest, with the adult coat), the pigment will reappear with its normal color.