Unless you know the pedigree of both birds it would be guess work.Green is the dominant colour.
The blue bird will have to carry the pied gene to breed pieds and the green bird must be split blue to breed blue young.It is a case of wait and see.
problematic step look on to google or bing just that might help
I have a dark blue budgie wich is female and a recessive green pied wich is the male and one egg has already hatched today
