Infrared (IR) illumination can be used to diminish colour effects in monochrome images. The example shows three different views of the same set of coloured marker pens.
Now all colours (except brown and black) show more or less the same brightness level, offering the possibility to identify a black print on the markers with a much better contrast.
Infrared illumination can also be used to look through coloured prints to inspect the surface below. They can also be utilised in combination with infrared sensitive cameras to reduce the effects of ambient illumination, as common indoor ambient light sources tend to have a low IR content. It should be remembered however, that this technique will not work in sunlight, as the sun has high levels of IR light in its spectrum.