Colour is not a property which is a physical part of things we see, it is simply the effect of visible light waves bouncing off or passing through the numerous objects in its path. The colour of an object is determined by several things, the characteristics of the light source, the way the object reflects, absorbs or transmits the light waves striking it. Sometimes, however, the effect of surroundings on the eye and mind and the physical condition of the observer can affect the perception of colour. Hence the eye is not always the best device to use for controlling colour in industry, where consistency of colour is all important.