1) Color 
A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components. When this model is associated with a precise description of how the components are to be interpreted (viewing conditions, etc.), the resulting set of colors is called color space....
A method of specifying a color (position) in color space, often using a coordinate system. Examples include RGB and the Munsell Color System.