Cool... they wont be austoxeable at hatch, But.... with leghorn blood you can see the males will have larger combs even at hatch. all of them will be white
The Blue egg shell gene(O) is carried by both gender, this gene is Autosomal(no sexlink) and both of genders carry 2 copies of it, so in this case if he use a maran rooster over a Cream Legbar hen then the hens of this cross will carry one copy of the blue egg shell gene
that will all depend on the type of maran...
CCL male crossed with a cuckoo maran female will produce cuckoo maran looking chicks and will look like cuckoo maran when adults but with a leaner body, the hens will lay nice dark green eggs.
if crossed with to black copper marans(CCL roo x BCM...
any breed cross to Legbars should come out looking Barred(except when crossed to white leghorn)... cross a legbar rooster to black Ameraucana, and you will end up with barred chicks... cross a legbar rooster with a silver/gold duckwing Ameraucana will produce Crele birds...