The differance between the male and female budgies?

I thought I bought 2 males, but late they have been fighting and my one budgies nose is not blue like it was.My other one is a very light blue the other one turned like a brownish.We got them a a month old.My question is can it change color and turn out to be a female?Sammy is the sweetest bird but Bobbie is always being mean and bites at you when you put your hand in the cage.They are now about 3 months old.Please help me understand if I have 2 boys or one of each.My dad was telling me about a blow hole but I could not find it.