The following series of images shows the output from a monochrome camera when different coloured objects are illuminated with red, green and blue light.
As can be seen, a monochrome camera picks up differing intensities dependent on the colour of the illumination used. When using colour cameras, similar rules apply. Therefore it is important that the illumination has all colours (RGB) and that they are present in the correct amounts, otherwise the camera will see different colours at different intensities, upsetting the colour balance. The hue of the light is often referred to as the colour temperature.
The graph shows the different colour spectra for white illumination sources used in machine vision. As LED sources become more popular its worth noting the difference compared to the older illumination sources.