A colour space is a method by which we can specify, create and visualise colour. As humans, we may define a colour by its attributes of brightness, hue and colourfulness. A computer will describe a colour stimulus in terms of the excitations of red, green and blue phosphors on the CRT faceplate. A printing press descibes a colour stimulus in terms of the reflectance and absorbance of cyan, magenta, yellow and black inks on the paper. Such a colour is usually specified by using three coordinates, or attributes, which represent its position within a specific colour space. These coordinates do not tell us what the colour looks like, only where the colour is located within a particular colour space.