Sexing Kittens by Color

Question
My daughter-in-law's cat gave birth to four healthy, darling kittens early yesterday morning.  We've read about how to sex kittens but it's very hard this early.  
The mamma is a Black Long Hair with a white locket.  The daddy is a bi-colored white/red Tabby.

One of the kittens is a tortie so we know she's a girl.  We have two Black and White Tuxedo kittens and one solid blue.  Could this give us a clue in knowing what sex they might be?

Also, I want to thank all the experts on this site.  I read and read this site for weeks and I you all gave such great information  and sound advice that I owe soooo much to you all! My daughter-in-law and I felt so much more confident it knowing how to support this pregnancy and the next few months of kitten rearing!!  Thank you from the bottom of my heart!

Answer
Cyndi,

Thank you for the vote of confidence.

The bad news is, although rare, the color of the cat determining the gender of the cat is not foolproof. Normally, cats with two colors (tortoiseshell, calico, and all their derived colors and patterns) are female, but they can, occasionally, be male.

With kittens, you lift the tail and see if the back end looks like a punctuation mark.

In males, the back end should look like a colon (:), where the top dot is the anus and the bottom dot is the penile sheath.

In females the back end should look like an upside down exclamation point (!), there the dot is the anus and the line is the entrance to the vagina.

Check the tortie first, if she is indeed a girl, than those whose back end look like hers are also girls and those whose back ends do not are boys.

I find at birth it is easiest to tell and then gets difficult until they are a couple of weeks of age.

Best regards... Norm.