Yesterday I had posted a workflow tip on how to use Natron Despiller Node to help generate a matte or mask with green/blue screen footage. Another node that somewhat perform the same operations as the Despillers is called Color Suppression Node. Accept the Color Suppression Node has an extended hue range of colors that are Cyan, Magenta and Yellow. See image below.
This Node can suppress colors that falls within the Additive and Subtractive concepts. You may also see that it has an output feature that displays its suppression results different from the Despillers. The Color Suppression Node’s options are Image, Alpha and Image and Alpha. The Despillers has a option like Spillmap to Alpha and other wordings base on the Depiller developer. Though the workflow is vastly different in concept as oppose to the Despiller nodes, you still get a pretty good reversed matte that can be scaled by crushing your blacks and whites to get an alternative key. The image below is a test workflow that is similar to Despillers nodes and other basic concepts.
If you have other workflows that you may find useful using the Despiller and Color Suppression nodes, please post them at your leisure.