No matter what container you use, make sure the paint is mixed well before you transfer. If it has been more than a day since it was mixed, then mix it again. Otherwise the pigment will settle and you'll transfer over a slightly different color. Also keep in mind this is only useful for a few years at most. The paint on your wall changes color with exposure to light, moisture, and oxygen. After a long enough period, even if you use the exact same paint, it won't match.