Old brickwork should not be painted. Modern paints are generally not vapour permeable and can cause damage as well as looking unsightly.
Stucco-work in London is traditionally painted and, since the 19th century, a cream colour has been the most popular shade, though stone colour is more authentic. Brilliant white paint is best avoided and a deep cream is usually preferable. The Crown Estate and the Grosvenor Estate both use Buttermilk in Regent’s Park and Belgravia (BS 08C 31, British Standard Colour) and this gives a good effect.
A good rule of thumb for old buildings is that stucco, woodwork and ironwork were always painted, but external brickwork and stone rarely were.