This is an updated Nuke version of the macro I worte for Shake a few years back. Splits any image into primary secondary and tertiary colours, ie red-green-blue, cyan-magenta-yellow, blacks and white (The last  is split into neutrals and white, which is user definable),
and gives you colour control of each one. You can also use it as matte outputs if you want.

Also included is a vibrancy node for more subtle saturation control. 'Secondary Colour' is dependent on vibrancy but it is also included as a separate tool.

Howard