Color filters and colored sources change which inks survive. A red filter on white light, or a red source, brightens red print and darkens inks that absorb red. A card with colored patches makes letters or blocks swap brightness as filters change. Match the illumination to the feature you need to lift or suppress. Near-infrared is invisible to people, which helps with comfort and sometimes with inks that vanish in the visible. UV fluorescence is the inverse. The source excites a pigment, the pigment re-emits visible light, and a UV-cut filter keeps the excitation out of the camera. A second bandpass can pass only the glow color.
Special lenses and sensors are required at the extremes if focus is to survive. Monochrome cameras plus filters are often more stable than color cameras for this work, because they measure the contrast you designed rather than a reconstructed color image.