ColorNegate[image] gives the negative of image, in which all colors have been negated.
ColorSelectorSettings -> {opt -> val} is a global option that specifies settings for the Color dialog box.
ColorSpace is an option for Image and related functions that specifies the color space to which color values refer.
ConfigurationPath is a global option that specifies which directories are searched for systemwide configuration information.
Congruent[x, y, ...] displays as x \[Congruent] y \[Congruent] ....
Context
(Built-in Mathematica Symbol) Context[] gives the current context. Context[symbol] gives the context in which a symbol appears.
Contexts[] gives a list of all contexts. Contexts["string"] gives a list of the contexts that match the string.
ContinuousTimeModelQ[expr] gives True if expr is a continuous-time StateSpaceModel or TransferFunctionModel object, and False otherwise.
ControllerInformation[] gives dynamically updated information on currently connected controller devices.
ConwayGroupCo1[] represents the sporadic simple Conway group Co_1.