There are three different types of metamerism (metamerism failure), or colour instability problems, which are important to know about when working with colour; observer metamerism failure, Illuminant metamerism failure and color inconstancy.

· Observer metamerism failure
When two observers (person, scanner or camera) see the same colour differently.

This occurs when different sensors (Eyes, CCD, CMOS sensors) perceive light differently, under the same light source.

· Illuminant metamerism failure
When two different objects is percieved as similar under one light source but different under another.

· Color inconstancy
If one is discussing a single print that seem to change colour depending on the light source. It is more accurate to say it has bad color constancy properties or that it has color inconstancy.

Only when you have two samples that appear similar under one lightsource but different under another, is it accurate to call it metamerism failure. All materials change colour depending on the light source, but the degree of change differ somewhat. Certain materials, such as carbon, is neutral black under almost all common light sources.

Other materials can change apperance to a degree that will seem unreasonable to most people. Printers using pigmented inks frequently have problems with colour constancy. For example monochrome images can appear green in daylight and neutral under tungsten lighting. Other colours can change lightness and colour, depending on the lightsource it is viewed under.

Improving Color Constancy properties

By using a RIP (a CMYK printer driver) as opposed to a Quickdraw or GDI driver, Pixl (and obviously others who know how to do this) can build profiles that will increase color constancy (stability) considerably, and thus minimise apparent colorshifts in many popular inkjet printers. This will make prints much more stable under different lightsources (more so than a regular C- print).