Cockatiels come in many different variations, including:

Normal Gray

This is the most common type of cockatiel. Below is Rembrandt, the normal gray I got for my tenth birthday.

Rembrandt, my normal gray.

Pied

In the pied mutation, colors are not distributed the way they are in other mutations. Their colors vary from bird to bird, but their faces usually have gray feathers mixed in while their bodies have lighter feathers mixed in.

This photo was found at Flickr.com.

Lutino

Lutinos are a beautiful mutation with no gray at all in them. They are bright yellow with bright orange cheeks. Females and males look exactly the same in the Lutino breed.

This photo was found at Flickr.com

Whiteface

Whiteface cockatiels are perhaps the most sought-after mutation. Their complete absence of color makes them very different from the other breeds, giving them an elegant appeal.

This photo was found at Flickr.com