Thomas R Jefferys wrote:

In lieu of any evidence to the contrary, I've been assuming that Genma has
brown eyes (and would have had black hair).  Kind of makes you wonder how
they ended up with a boy with BLUE eyes.  ^_-

Easy. Blue eyes is a recessive trait, and both Genma and Nodoka are
heterozygous. They carry both the brown eye allele and the blue eye allele,
and the brown eye allele is dominant. That means that its perfectly
possible for a couple both with brown eyes to have a child that is
blue-eyed.

Next time, choose a more challenging problem. :)

You mean such as how these recessive blue eyed genes show up so
prominently in the Japanese gene pool?  Personally I prefer to
ponder other mysteries, such as the riddle of why I and only I
am blind to the blueness of Ranma's eyes.  That color is the 
one I personally call "grey".  His female form  (in the anime)
to be sure does have a colour I call "blue", and I have even 
read people who seem to think the two forms have the same eye
colour, when their eyes seem very different in colour to me.

Bearing this in mind it is doubtless worthless for me to say
that Genma's eyes, (being drawn without a visible iris) can only
be called black, that Kuno's eyes seem to vary between black and
grey, Kodachi's eyes are obviously grey (to me), and Nodoka's eyes
are the colour of Akanes, the colour I call dark brown.  

To be sure, I have to take the anime with a grain of salt anyway.
Consider Ranma's female form.  Does she have red hair just because
she's drawn that way?  If she doesn't, how did Kuno mistake her for 
otoko-Ranma from the rear?  How come he never composes an ode 
comparing her hair to the sunrise of his love?

Then there's the girls from Area 88, who reveal the startling news
that all good looking girls (and a fair chunk of the guys) are natural
blondes.  Go fig.  It still sends chills down my spine when people
describe the maroon colour of Priss's eyes (mostly brown with a little
red) as being red, as some character moons over her compassion and
attractiveness.  My reaction tends to be "AAAH!  A vampire!  Demon 
possession."  It takes me a moment to realise their talking about her
regular eye colour, which I generally think of as brown (because maroon
is still a pretty strange eye colour, even if you aren't Japanese.).