For an accurate color, paint it exactly as you WILL be painting them. If you are stripping down to bare wood first, then strip down to bare wood and paint over it. If you are painting over an existing finish, then apply your samples over the existing finish. By doing so, you will not only know the final color but you will also no how much work you are going to be in for, i.e. how many coats, etc.
Also, when applying test samples, I always try to paint a flat area that is easy to sand off later if it isn't the color you want. Don't put it into nooks and crevices because it will take much longer to remove it later or cause you to put more coats over the top to cover up the different area.