If you are planning to redecorate a room in a period house two techniques can be useful:
There are two tools; one uses the power of Flash 6 and the other for non-Flash users.
Note that this is not an exact science; the colour on your computer screen will not match a swatch exactly because of the screen and because of the swatch printing process. And the colour on your wall will look different depending on the base coat and on lighting in the room. However, it will give you an idea!