Creative combinations for matting are endless given the extensive range of colors and surface textures available in matboard. When selecting a mat it should complement and not detract from your artwork. Whenever possible lay the artwork next to the matboard. This is more accurate than trying to remember the artwork's colors.
Remember, there is a relationship between the value of the mat and the value of the artwork. (Value is how light or how dark it is.) Selecting the matboard defines that relationship. How do you want the mats to work with the artwork?
One of the safest choices is a color in the medium overall value of the the artwork. To get the medium overall value, match the mat value with the value of the predominant colors in the artwork. If you choose a mat that is too light, the artwork will appear to jump out of the mat. If you choose a mat that is too dark, the artwork will look constricted. Usually the color of the mat will be either a tint or a shade.* Colors high in saturation (not tinted or shaded) will tend to dominate an artwork and are better used as accents in multiple mat designs. High saturation colors may be used to produce a strong contrast. The objective in selecting mats is to enhance the artwork, so the viewer's eye is drawn to the artwork and not to the mats or frame.
In multiple mat designs, visual stability is created when the top mat is the same overall value as the artwork. For the artwork to recede, the top mat is the darkest value, and the undermats get lighter as they near the picture.
For the artwork to come forward, the top mat needs to be a lighter value than the artwork and the undermat near the artwork should be considerably darker.
A color will seem to change depending on what color is next to it. Purple will appear more blue when placed next to red. Purple will appear more red when placed next to green.
Value is also changeable. A color that appears dark when surrounded by white will appear much lighter if surrounded by black.
Note: Some juried shows require artwork to be matted only in white mats with no texture. The reason is that any color put on a mat changes the appearance of the colors in the artwork. Try different combinations of matboard next to your own artwork, or ask your local art store or picture framer for suggestions.
For more detailed information read: The Framer's Book by Paul Fredrick, CPF
*A tint is a color with white added to make it a lighter value. A shade is a color grayed to make it a darker value.