If you want to sex chicks, the easiest way is to have a breed (though I
think the ones that have sex-linked color differences are mainly crosses)
that produces differently colored males and females.
I'm much impressed with the Golden Comet -- the males are yellow fluffies
when hatched (and turn into huge white cockerels with some black feathers)
and the females are reddish-brown (and produce incredibly large eggs.
All the big hatcheries hire people who are good at sexing day-old chicks,
and they must be pretty good; regardless of hatchery, I've gotten few
cockerels when I ordered pullets.