You can use the coloring rules for mixes, sure! There's a whole thread on sexing EEs this way. It gets a bit less obvious on some color combinations but if you know what to look for, chicks that start life as chipmunks can be sexed by feather patterns at 3-4 weeks.
BTW, I think hatcheries cross in brown Leghorns to boost productivity. I've seen a pretty huge variation in comb size and body build that screams Leghorn influence.
BTW, I think hatcheries cross in brown Leghorns to boost productivity. I've seen a pretty huge variation in comb size and body build that screams Leghorn influence.