Identifying cat genders in the field - coloration

1. We're interested in identifying which cats are female, because.... females have the kittens.  Selective trapping and spaying of the female cats can stop reproduction and growth of the colony immediately.   Immediately, is good.

a classic "patchy" calico - black, orange and white in solid patches of color.

A calico tending toward a tortoiseshell - lots of black, less white.

A tortoiseshell calico - no white.

a muted, or dilute calico: gray, tan and white

Looks like a tabby, but has orange mixed in, so she's a calico.  Sometimes called a "torbie".

Tortie - her orange might be faded, or she might be almost entirely black with one small orange spot or a few hairs!  still female.

I call this a calico tuxedo, because of her white feet.

2. Orange, or orange-and-white cats are often male (75%), but can be female.  

this guy looks male - long limbs.  He's less than 2 because he doesn't yet have jowls.

this girl is a mom - note her calico kitten.

Identifying cat genders in the field - cat butts

A cat's gender is written on its bottom - can you read it?

Un-neutered male, younger than 2 years (no jowls).  Starting at about 8 months old, you'll also observe that he'll spray to mark his testosterone-y scent.
I think he's showing them off.

Neutered male.  When neutered young, there's no visible scrotum.  This boy has 4 "spots" - top one is his anus, bottom one is his pee pee, looking closely, the middle pair are his former testis (highlighted by his coloration).

Same here.  Neutered male - 3 dots.  Note the distance of his peepee from his anus. 

A tomcat - un-neutered male over 2 years old.
Raggedy ears from fighting, the large "grapefruit" sized head, the jowls develop at 2 years + and will disappear after he's neutered. I admit he has bits of orange which might make you think he was a calico, if it weren't for his FACE.

A (goofy) female.  No way to tell if she's spayed.  Often her vagina will be highlighted by her coloration, and it looks like a slit immediately below her anus (visible here).  Male's "stuff" is an inch or more from the anus.