Yes, it is. If the wall you wish to paint is in good condition and the paints are chemically the same, for instance, the old paint is acrylic, and the paint you want to use is also acrylic. However, both paints must be of the same shade to give a perfect result. It is, however, possible to use a primer to adequately cover the old color, then apply one or two coats of the new paint you wish to use.