Blue is rare because it is associated with auto-immune problems. True blue dogs, which are actually dilutes, tend to have clumping of white blood cells. This phenomenon is associated with the dilution of pigment. Problems such as Alapecha (hair loss) manifest as a result. While the color may be pretty and it can be healthy, it is generally difficult to retain health when dealing with true blues. Most dogs that are called blue are actually due to the G series, the graying gene, and a gray and blue can look alike, phenotypically, but real blues, dilutes (which are found in doberman and chihuahuas), are subject to the health problems that go with the color. Blue Chihuahuas are not something you want to pay "Extra" for.
