Some people wonder if any of the painting companies do a paint color match themselves. If a painting contractor color matching paint for one of his customers, he would have to do it the same way a customer would. Which is taking a sample of paint and brining it to a paint store. There is a couple of requirements to a sample, for a color match to be successful. If a customer has a sample of actual paint that needs to be matched, that would be the easiest color match for a paint store to do. If actual paint sample is unavailable, next best thing is a piece of drywall, stucco or wood. Sample needs to be big enough, so that the computer can read the color easily. Usually a sample the size of a credit card is good enough. It is best to get a color sample from inconspicuous place where the hole can be patched and painted after.
For matching the wall color, a piece of drywall can be cut out just about any place below the eye level.
If a color match needs to be done for doors, trim or baseboards (those usually all same color) best option it to take down one of the doors, and take it to the paint store, instead of trying to cut out a piece of wood from trim or baseboard.
If a color match is for the ceiling, to cut out a piece of drywall in a ceiling of the closet (if it is the same color as main area) may be the best option.
If the color match is needed for exterior it is best to get a sample that was affected by the weather the least (not the bottom of the house).
One of the worst samples to bring to a paint store for a color match is sample of glossy paper, from a magazine, for example. Those are very glossy and a computer can't read them. For a color match to come out right, it has to be an actual sample, where the desired color has been previously applied to an object.