The same is true of black cats, the other way around. There are fewer orange (or black) female cats because female cats have another option of coloring - tortoise shell (no spots) or calico (with spots). Another way of phrasing it, half of the male cats are orange, the other half are black - female cats have a third option.

Side bit - the wiki page for X chromosome inactivation shows a picture of a tortoise shell cat. https://en.wikipedia.org/wiki/X-inactivation

http://messybeast.com/tricolours.htm

And white spots gets into interesting questions of embryonic cell differentiation http://messybeast.com/bicolours.htm

The "why are there large splotches of color with a calico cat compared to the much more mottled color pattern of a tortoise shell cat?"

http://messybeast.com/genetics-index.htm has a deep rabbit hole to go down (and that's for domestic cats... http://messybeast.com/wildcats-index.htm for the other cats).