It was a chromacake called Landscape Green. It's Brushed on when combined with water using a Japanese Makeup Brush. Then, they use a lighter green, which has more of a blue tint to it to highlight her nose, cheeks, and other highlighted parts of her face. They use a purple shade, can't remember the name for contouring, and eyeshadow, they also had a silvery shade for highlighting of her eyelids. After this, they covered everything with a powder called Golden Olive to make the landscape green look a bit more like skin, and to dampen the brightness of the landscape green.

You can only attain some of the shades by calling a 1-800 number that any MAC stand in a retail store can give you. It's on their cards, or probably on their website.
But yes, the Wicked Witch is a totally different character. Having designed the makeup for this character for a production I did, it should be a brighter green, with harder angles, prosthetic warts, and even if you can... a prosthetic chin, because it's an iconic character.
Hope that helps.
that's a really big mic...