Muted calicoes are cats with blue, cream and white fur. It's a color pattern, not a breed. These cats, also called diluted calicoes, have genes for multi-coloring, piebalding and color dilution. They're almost always female. Male muted calicoes are rare, and almost always sterile.
What Makes a Calico?
Cats carry genes for orange- or black-colored coats on their X chromosomes. Female cats, by definition, have two X chromosomes, and sometimes they get genes for both orange and black fur. One of the genes is randomly inactivated -- a process called lyonization -- so they get spots with either fur color. Cats with orange and black fur are called tortoiseshells.
Cats also carry separate genes for unpigmented, white fur. Both male and female cats can have patches of white fur, which is called piebalding. Tortoiseshell with piebalding are called calicoes.
What Makes a Muted Calico?
Cats also carry genes for color dilution. When one such variation is expressed, an orange coat color becomes cream and black becomes gray, which is called blue among cat fanciers.
There are other color-mitigating genes at other loci -- black can become chocolate or red, for instance -- but it's cream-blue dilation that's of concern. This recessive trait causes clumping and uneven pigment distribution, which results in lighter fur coloration.
Calicoes with cream-blue dilutions are called muted calicoes.
Breeds and Variations
Muted calicoes have a common coloring, not a common breed.
Many such cats are domestic shorthairs -- the so-called mutt of the cat world -- but they don't have a monopoly on cream, blue and white fur. Manx and Persian cats, for instance, can have muted calico coats.
While most tri-color cats are calicoes, a few, including the tri-color Bengal, aren't. All muted calicoes, however, are calicoes. Because of the wide range of applicable breeds, muted calicoes have no common size or temperament.
Male Muted Calicos
Male cats have one X chromosome, so they generally can't have the both orange and black fur necessary to be calicoes or cream and blue fur necessary to be muted calicoes.
There is a condition, called Klinefelter syndrome, in which male cats get an extra X chromosome, thus opening up a variety of color variations, including calico and muted calico coloring. The condition itself renders the male cats sterile, unless they have another genetic anomaly that's rarer still.