Basically and simply, there is a Cr gene or champagne gene that causes [severe to moderate] dilution to occur. This is the same gene/allele that is found in most mammals and studied most extensively in albino horses, which are by the way, NOT true albinos as they do not have pink eyes that totally lack pigmentation. They are creme just as your "white tigers" and "white" Dobermans are---excessively diluted individuals correctly called cremellos and perlinos based on the form of their actual color mutation, but the effects on all mammals are genetically the same. This Cr gene causes a light iris coloration AND for the nose leather to fade especially in winter. While others are born with color and stay that way, these creme/champagne offspring are generally born white or near white and they tend to gradually "color" with age. (This coloring up effect is generally seen in lighter colored palomino horses and is caused from the same cr gene.) This coloring up is how you can determine if this cr gene is present in an individual.
Any dog with this cr/creme coloration should be bred only to a black and white tri...depending on the true genotype of the tri parent, you'll get a wide variety of colors in your offspring as this cr gene can mix AND dilute ANY color or pattern including excessive dilutes that are what are considered ALBINOS in dogdom and are a breed disqualification--- and these double dilutes also are capable of producing the genetic defects of the lethal white syndrome.... when this cr gene is doubled in pairs the cr/cr individual dies in utero, is stillborn or dies shortly after birth.
In genetics there are only two colors, red and black. All others are only variations of intensities.
The diluted intensities of these recessive colorations come from repetitively breeding recessive colors without occasionally going back to the darker and much needed, black. When recessive alleles are paired in doubles, they cause the base colors to be dramatically lightened in the individual: cafe au lait, lemon, silver, fawn, creme etc..
You can breed blues which are a dilute of black or chocolates which are also a diluted coloration, to another individual of their same color factor and get a good dark blues or chocolates, BUT the chances are according to the laws of probability that only a 25% will be as dark as the darkest parent, 50% will be a color intensity somewhere between the colors of both parents and 25% will be lighter than the lightest parent. Parents can only pass on those gene that they have, and each offspring only receives half of each parents DNA, so these figures can and do change according to how the genes are paired, and with these dilutes THEY must be paired for the individual to exhibit them. But the basic rule is the lighter the individual, the lighter their offspring can be and we are not trying to produce albinos.
Black is dominate, but our breed is heterozygous, having many colors and the genes for them. The best and most efficiently way to get "good colors" is to ideally breed your dilutes to a tri with black that has a parent, or one or more grandparent/s of the coloration you wish to produce. Your number of colored offspring will vary depending of the actual genotype of the pair you breed, and you may get some tri's with black, BUT the offspring will be darkly hued and these tri's with black will also have these recessive genes in their genetic makeup which will allow you to use them in your breeding programs to get those colorations you want in more quanities. With repetitive breeding and culling, you can develop a family of homozygous dogs that will produce only chocolates, or blues or apricots/orange etc. But you have to do it this way to develop DOMINATE recessives families of dogs. This is how they developed the red Dobermans, the red/liver Springer Spaniels, and even the double recessive colorations of the Weimaraner from those early dogs of liver German Pointer breedings.Color can be of a lethal (or delayed lethal as in the gray's which RT's are not known to have) variety, but the effect of color on the immune system is generally related to other factors.
