Re: Is it true that tri-color male cats are frequently sterile?

Yes.  Cat colors are determined by genetics.  Like in humans, a cat's 
gender is determined by the chromosomes it gets from it's parents, an X 
from its mother and an X or a Y from its father.  XX is a female and XY is 
a male.  

The gene that determines the orange color is called O and can only 
be attached to the X chromosome.  OO means the cat will be a tricolor, also 
called calico or tortoiseshell.  To get an OO pattern means that the cat 
must have two X chromosomes and must be female.  Occasionally a flaw will 
occur and the cat will get two Xs and a Y, XXY.  This can cause a male 
tricolor cat which is almost always sterile.  Human men can also get this, 
called Klinefelter syndrome, which also causes them to be sterile.
For more information and a really good explanation of this go to 

 http://www.io.com/~tittle/cat-faqs/tricolors.html