My guess is female, but it can be hard to tell with the lighter colors of parakeets. If the blue one is more than a year old, it's probably a male. If it's still young, it might be female also.
GENERALLY speaking you can go by the color of the cere - the fleshy part above the beak where the nostrils are. If the cere is blue it's usually male, pink, white or light brown is female - but that's not 100% depending on the color of the birds.
In really young birds the cere color is even less reliable. Look at the nostrils. In a very young female, the area of the cere above the nostrils will be almost transparent or more whitish around them where in a males they will be more opaque.
It looks like there is a whitish sheen to the nostrils - that along with the pink color makes me guess female.
As females become sexually mature their cere will usually darken significantly. Once my ladies start laying eggs and raising babies their ceres will become either very washed out pinkish in the lighter birds or completely brown and crusty looking in the darker birds.
Also temperment can tell you a lot. Male baby budgies (not hand raised, but parent raised like most petshop birds) tend to be much gentler when handled. Females will almost always screetch and bite even from a very young age. A sweet laid back baby is almost always male.
Hope this helps!
Enjoy your birds. I have an aviary outdoors with a flock of parakeets. It's really amazing how their behavior changes when they have a flock and the room of a true flight cage.
Check out my webcam to see my budgies... link in my signature below.