Cockatiels have two pigments that cause color in them: melanin causes the gray, and lipochrome causes yellow and orange. Peeper (right, photo by me or my dad) was a typically colored cockatiel (called gray), and posessed both melatonin and lipochrome.
Lutino (like Gabe, left, photo by Tammy) is a mutation where they don't have the melatonin, kinda a "half-albino," so anywhere they would've been gray is white instead, and his eyes are red (even without the flash) instead of brown. They still have the lipochrome so retain the yellow head and tail, and orange cheeks.
Whitefaces (right) do have the melanin so they have gray backs and sides, but don't have the lipochrome so their heads are pure white.
In order to get a true albino (Trina, left, photo by
There are actually many more colorations to 'tiels than just these four that I mentioned, but they're a basic start.
And just because no list of bird photos is complete without it, here's some babies!
The above photos for normal gray and lutino were of my own birds, the albino is