Apple Color 1.0 - Manual (Page 237)

Chapter 11 Color FX 237
You can think of a node tree as a waterfall of image processing data. Image processing
operations begin at the top, and cascade down, from node to node. Each node exerts
its effect on the image that’s output from the node above it, until the bottom is
reached, at which point the image is at its final state.
The very last node in any node tree must be the Output node. This is the node that
sends the image that’s been processed by the Color FX room back into the Color image
processing pipeline. If there is no Output node, or if the Output node is disconnected,
then the node tree will have no effect on that shot, and its effect will not be rendered
by the Render Queue.
Note: A CFX bar will only appear in the grades track for clips with connected Output
nodes.
Node Inputs and Outputs
Single input nodes take the image and perform an operation upon it. Single input
nodes may only process one incoming image at a time, and so you can only connect a
single noodle to any one input.
Multi-input nodes are designed to combine multiple variations of the image in
different ways, in order to produce a single combined effect. These nodes provide
multiple inputs so that you can connect multiple noodles.