Color matching is important and we take great pride in our ability to produce critical color matches. Unfortunately, this isn't always possible. I'd like to discuss several of the reasons why exact matching may not be possible.
1. Pigments aren't available. This is becoming more and more of an issue, as regulations are limiting the pigments that are used in paints and coatings. This first began to affect us several years ago, when certain chromium based reds, yellows, blues and greens were made illegal in California. There are close, but not exact, duplicates of these pigments—so a bright, deep red, like the old Ferrari Testa Rosa, is not achievable—it is slightly off; not quite as intense, maybe a bit to orange. This is industry wide, and rapidly becoming both nation and worldwide, so the stricter California regulations are not as outlying as they once were.
Just recently another category of pigments (also heavy-metal based) have also been removed from use—and once our stock runs out, we will be further limited. We do try to order an extra back up amount of mixing paints before they are taken off market, but keeping paint for more than a year or so starts to add other issues.
2. Sample colors (say, Pantone swatches) are ink, rather than paint based. Ink is much more transparent than paint, so the reflection of the paper can boost the brightness of a color. So certain light, but bright colors are harder to achieve in paint. We do actually use dyes at times in our mixes, both for transparent tints (where they need to be used) and just to "bump" up the intensity of paints that need the extra oomph added, but there is only so far you can push a paint with dyes. (Plus dyes may not be as colorfast as we need then to be).
3. Colors can, and often do, vary greatly depending on what light they are shown in. If not specified, we match to mid-day open shade. We know some clients want direct sunlight, others want warm fluorescent, etc. lighting. We do have a Macbeth lightbox that we use to look at matches under specified conditions.
4. The texture of the finish will affect the color. It's not unusual for a client to want a very dark color in a matte finish. Even pure black, in a matte finish, reads as a dark grey.
5. Pearls and metallics offer even greater challenges. We use additives from several suppliers, but unlike pigments, the flakes that make paint metallic or pearlescent do not combine with each other—they remain separate specks. So if we need to make a coffee brown metallic that has a copper-gold fleck in it, we may not be able to get the same fleck that is in the sample you provide.
6. We do have tricks—for instance, we can do glazes of one transparent or translucent layer over another, which can greatly increase the range of colors and effects that we can get. But, if you are doing samples for production, will finishes that complicated be an option?