This Nuke plugin will help you pinpoint color values
outside or inside the defined boundaries.
Lower: Lower boundary value
Upper: Upper boundary value
InsideBoundaries: Displays the color range between Lower and Upper
LowerColor: Color to use for everything below Lower
UpperColor: Color to use for everything above Upper
InsideBoundariesColor: Color to use for everything between Lower and Upper
Source code included.
Compiled for Nuke7.0.5->linux64
Enjoy and drop me a line if you have any questions.