Here's why:
* Calico Pattern: The calico pattern is determined by the X chromosome. Female cats have two X chromosomes, while males have one X and one Y. The gene for coat color is located on the X chromosome. A calico cat has two different alleles for coat color on its X chromosomes, resulting in patches of black, orange, and white fur.
* White Fur: The white fur in calico cats is caused by a different gene, not related to the X chromosome. This gene determines whether the pigment cells in the skin and hair will produce color or not.
* Genetic Combination: To have a calico cat with no white, both X chromosomes would need to carry the genes for black and orange fur, and the white fur gene would have to be absent. This is a very unlikely combination.
In short, calico cats are always tri-colored, with white being a mandatory part of the pattern.