There are a few ways to tell the sex of a cockatiel. Firstly, and most presisly, there is DNA sexing. You can go to the local vet to have this done. Secondly is by behaviour. Males will be more vocal than females, and will whistle and talk, while female somewhat lack in that department. And thirdly, there is visual sexing, this only works with normal greys and some pieds. I know this does not apply to your bird, but it is good to keep in mind. If it is a young bird, then this will not apply, either. There will be bars under the tail and grey over the cheek patches if female, while males have bright, clean faces and fully grey tail feathers. Young birds will have dirty faces and bars. With pearls (yours isn't) males lose their marking as they age, while female keep theirs. Personally I think Buzza is a male. Hope this helps you, Ezza.
As ratzy said, Male and female cockatiels (of the normal gray variety) can be sexed by their coloration. A fully grown male cockatiel will normally have a bright yellow face, and bright orange cheek patches. Whereas, a female will look the same only it looks as if her face got dusty or dirty. She will also have yellow, cream, or even white barring under her tail; the male's tail will be solid gray on the top and the underside. You can still tell the difference with a whitefaced variety.
Lutino? In that case, DNA testing is going to be 100% accurate. But the quickest and less accurate way of telling is whether or not the bird still retained the barring on the tail. If so, it is a female. The barring will be very faint (because of the color variety), so look closely.
DNA isn't too bad over here... ALso if it is a cockatiel there is a pretty good chance eggs will come along in the first year or so if it's a girl. Not everyone has this problem but cockatiels can be very prolific layers, and it is not uncommon to come home to a bird fiercely guarding her new "nest"