As a pet budgie’s owner, you need to identify its sex firstly if you want to pair it with an opposite sex. The most simple and common way to identify a budgie’s sex is to observe its nose cere’s color. But budgies at different age have different colors.
An adult budgie who has pure white or dark blue or purple cere is surely a male, and an adult budgie who has a brown or giner yellow cere is surely a female. But the young budgie may be a little hard to indentify the sex for its cere’s color is not that pure/obvious , generally when the young budgie’s cere is while / pink and has a white cycle around the nostril should be a female, otherwise it’s a male.
The hard case is the cere appears white mainly with light blue at lower area, it’s often white around the nostril and then you judge it’s a female, but one or two months later, the blue on its cere may become darker, and then your judgement has to change. Actually it’s a male budgie, its “white” cere become blue because it grow up. And you can see the budgie often do head bobbing that looks like vomiting, this is a male parrot’s sexual behavior. So we can judge a budgie’s sex not only on its cere’s color, but also on its behaviors when he grow up to be an adult bird. Now let’s come back to the point: the cere appears white but with ligh blue at bottom is more possible a female actually, but you still need to wait one or two months to see its color changing and also put attention on its behaviors.
The below is more about the cere’s color at different situation to judge a budgie’s sex.
The adult female budgerigars in estrus.
The adult male budgerigars in estrus.
The adult female budgerigars who are still not in estrus.
The adult male budgerigars who are not in estrus yet.
The young male budgerigars who are not adult yet.
The young female budgerigars who are not adult yet. The ceres are white or white with the lower area are light blue, the area around the nostril is surely white. Please be noted that the budgies with ceres are basically white but the lower area are light blue, such budgies may need one or two more months to observe, see if the cere will turn into blue or dark blue to be male actually.