Disney Ink And Paint

My question is simple. What type of ink or paint was used on cels to shadows.i can take to make the darker shades on clothing, but im still baffled by how they originally added shadows cast by the characters. They are usually clear and virtually seamless look when u how it does not distort the background.

http://g-ecx.images-amazon.com/images/G/01/dvd/disney/pinocchio/Pinocchio1.jpg

thats a great example of what Im trying to achieve. if anyone has any answers or suggestions on what I can use that would be a great help. Thank you!

I think it's the same idea as the clothes: it seems that everything they did was to use a darker shade of green.

try to follow the contours of the background, instead of letting it run on the shadow.