Colouring:

The use of colours in CAD/CAM has two major objectives: facilitate creating geometry and display images. Colours may be utilized in geometric construction. In this case, several wireframe, surface, or solid entities may be assigned different colours to distinguish them. Colour is one of the two major ingredients (the second being texture) of shaded images produced by shading algorithms. In some of engineering applications such as finite element analysis, colours can be used effectively to display contour images such as stress or heat- flux contours.

Black and white raster displays provide achromatic colours while colour displays (or television sets) provide chromatic colour. Achromatic colours are explained as black, several levels of gray (dark or light gray), and white. The only attribute of achromatic light is its intensity, or amount. A scalar value between 0 (as black) and 1 (as white) is generally related with the intensity. Therefore, a medium gray is assigned a value of 0.5. For multiple-plane displays, different levels (scale) of gray may be produced. For instance, 256(28) different levels of gray (intensities) per pixel may be generated for an eight-plane display