Blue and white birds could turn out to be any colour really... I had a pair the same two colours and they ended up with 1 faded yellow with brown wings, I can't remember any more, but they were quite pretty. Most were yellow though, a faded yellow.
A yellow and green bird will probably end in a clutch of green chicks. Because green is a dominant colour in budgies, so the chicks are usually green. I bred a grey bird and a green bird before and the first clutch was all green, but their second clutch turned out to have one yellow one, one grey one (same as mother) and an albino!
My tips would be read up on breeding budgies! I recommend you don't try get the information off Y!A as it isn't all very helpful sometimes, I see some people abuse people when they ask... So just on other websites and stuff... Remember, the essentials are:
A good diet
A good environment
A good breeding box
And, well, a two good birds!
The birds must be healthy though, run them to the vet for a check up before breeding just to make sure they are healthy. Also, do NOT breed birds too young, if they are two years old or older, they are fine, but anything older than five years shouldn't be bred. So anything between the age of 2 and 5 is perfectly fine and ready for breeding.
OH! Sorry, a lot information, but budgies have life time mates, and budgies pair up with whoever they want, so there is no guarentee your yellow bird will pair up with the green one, and there is no guarentee your blue one will pair up with the white one. It isn't really your choice, so whatever the birds choose, is what they choose.
