A dilute calico kitty could be described as a white cat that decided to play around in watercolor paints instead of in bright oil paints. However, those splotches of blue and cream come from some pretty complicated genetics.
Calico
Calico is both a color and a pattern, but it is not a breed of cat. Many breeds and mixed breed cats can be calico, such as the American shorthair, American longhair, Manx, Japanese bobtail, Cornish Rex, Maine coon and Persian, to name just a few of the more popular breeds. A true calico cat not only has three different colors on its coat; one of the "colors" must be white, and the colors must appear in spots or patches, not closely intermingled with each other.
Dilute
"Dilute" simply means the color is less intense. For example, cream is the dilute version of red, and blue is the dilute version of black. Cream is a soft reddish color, like strawberry blond, and blue is a smoky gray color. Other dilute colors include lilac, which looks like a lighter version of blue but is actually the dilute of chocolate; and fawn, which appears beige and is the dilute of cinnamon.
Genetics
It takes a complex and confusing combination of genetic markers to create a dilute calico cat. The short explanation is that a dilute calico must inherit three specific genes: a mosaic gene that allows two basic colors to be expressed instead of only one; the dilute markers of the two basic colors; and a white spotting gene that causes parts of the coat to be white. Only when all of these markers are present can a cat be a dilute calico. Because basic or dense colors are dominant, most calico cats' coloring is dense instead of dilute, even if they carry dilute genes. It takes the expression of the recessive dilute genes to create a dilute calico.
Color Combinations
Even though a calico is described as having three colors, only certain color combinations are truly calico. For dense calico cats the combinations are white, black and red, sometimes referred to as orange; white, chocolate and red; or white, cinnamon and red. Along those same lines, dilute calico cats must be the dilute versions of their densely colored counterparts, such as white, blue and cream; white, lilac and cream; or white, fawn and cream.
Tortoiseshell and Patched Tabby
Sometimes calico cats are called torts or tortoiseshell, but there really is a difference in the coloring. Tortoiseshell cats have very little white; the white usually appears only as small spots on the face, paws or chest. Also, the red and black do not appear in distinct patches, but are intermingled in a brindle-type pattern. A patched tabby is a calico cat with the distinct tabby stripes within the black and orange patches.