So I enjoy that in the "Gallery of Tortie Types" there is a picture of "Calico at Christmas" because I know that is what my calico cat looks like every December 25th.

so the reason calico cats can only be female is that the gene for hair color is on the x chromosome and oonly one x chromosome is expressed in any given cell, and so you have patches. Male cats only have one version of the gene to express, so they are solid color. You didn't really want to know that, but, anyways. . .